GIFT  OF 

ASSOCIATED  ELECTRICAL   AND 
MECHANICAL   ENGINEERS 


MECHANICS  DEPARTMENT 


A 
•  JL-i. 


PRACTICAL  USES 

OF  THE 

WAVE  METER  IN  WIRELESS  TELEGRAPHY 


McGraw-Hill  BookCompany 


Electrical  World         ^Engineering  and  Mining  Journal 
Engineering  Record  Engineering  News 

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Metallurgical  and  Chemical  Engineering  P  o  we  r 


PRACTICAL  USES 

OF  THE 

WAVE    METER 


IN 


WIRELESS   TELEGRAPHY 


BY 

J.  0.  MAUBORGNE 

FIRST   LIEUTENANT   24TH   U.    8.   INPANTET 
FORMERLY   INSTRUCTOR,    ARMY   SIGNAL   SCHOOL,  FORT   LEAVENWORTH,    KANSAS 


McGRAW-HILL  BOOK  COMPANY,  INC. 
239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 

1913 


Engineering 
Library 


cr 

V 

MECHANICS  DEPI. 

COPYRIGHT,  1913,  BY  THE 
MCGRAW-HILL  BOOK  COMPANY,  INC. 


TUB. MAPLE. PEESS.TOKK. PA 


PREFACE 

In  its  original  form  this  work  was  first  privately  printed  for 
reference  use  at  the  Army  Signal  School,  Fort  Leavenworth, 
Kansas,  and,  in  1912,  was,  by  direction  of  the  Secretary  of 
War,  adopted  for  use  at  that  school. 

The  text  has  since  been  carefully  revised  and  amended,  and 
in  its  present  form  is  now  published  for  commercial  and  technical 
school  use. 

The  author  desires  to  acknowledge  his  indebtedness  to  Prof. 
G.  W.  Pierce  for  his  careful  criticism  of  the  manuscript  and  for 
the  many  suggestions  that  have  added  materially  to  the  correct- 
ness of  the  present  edition.  The  author's  thanks  are  also  due 
to  Mr.  E.  R.  Cram,  Radio  Engineer,  U.  S.  Signal  Corps,  for  many 
valuable  suggestions  regarding  the  revision,  and  to  Major 
Edgar  Russel,  Signal  Corps,  U.  S.  A.,  for  his  kind  assistance 
and  encouragement. 

The  literature  of  the  Telefunken  Wireless  Telegraph  Company 
has  been  freely  consulted  in  preparing  the  data  on  the  meters  of 
that  Company. 

J.  0.  M. 

GALVESTON,  TEXAS, 
October  1,  1913. 


749205 


CONTENTS 

PAQE 

PREFACE v 

CHAPTER  I 


GENERAL  REMARKS 1 

Definitions. 

Alternating  Current. 

Amplitude. 

Logarithmic  Decrement. 

Damped  Oscillations. 

Oscillatory  Circuit. 

Oscillation  Cnstant. 

Syntonic  Circuits. 

Operation  of  the  Wave  Meter. 

Wave  Metor  Circuits. 
The  Wave  Meter  as  a  Receiving  Device. 
The  Wave  Meter  as  a  Sending  Set. 

CHAPTER  II 

TYPES  OF  WAVE  METERS  IN  USE  IN  THE  U.  S.  SIGNAL  CORPS     ...     11 
The  Pierce  Wave  Meter. 
Telefunken  Wave  Meter  Type  E.  KI.  W. 
The  Type  E.  Ki.  Wk.  Meter. 
Large  Telefunken  Wave  Meter,  Type  E.  G.  W. 

CHAPTER  III 

USES  OF  WAVS  METERS;  MEASUREMENTS  OF  WAVE  LENGTHS    ...     20 
The  Wave  Meter  Used  as  a  Receiving  Set. 
General. 

Measurement  with  Helium  Tube. 

Measurement  with  Telephone  and  Detector,  or  Galvanometer  and 
Detector. 

CHAPTER  IV 

TUNING  THE  SENDING  STATION 22 

Measurement  of  the  Wa.ve  Lengths  of  the  Coupled  System. 

Resonance  Curves. 

Calculation  of  the  Percentage  of  Coupling  of  a  Coupled  System. 

CHAPTER  V 

MEASUREMENT  OF  DAMPING  AND  LOGARITHMIC  DECREMENT    ....     31 
MEASUREMENT  OF  DAMPING  OF  A  CLOSED  OSCILLATORY  CIRCUIT     ...     34 
Using  Wave  Meter  with  Galvanometer  and  Ther mo-element. 

vii 


viii  CONTENTS 

PAGE 

Damping  Measurement  using  Thermoammeter  instead  of  Gal- 
vanometer. 

Damping  Measurement  using  Hot-wire  Wattmeter. 

Determination  of  the  Self-damping  of  the  Wave  Meter. 

To  Find  Damping  of  the  Wave  Meter. 

Using  Thermo-element  and  Galvanometer. 

To  Find  Damping  of  Wave  Meter  using  Thermoammeter. 

To  Find  Damping  of  the  Wave  Meter  using  the  Wattmeter. 

Determination  of  the  Resistance  of  the  Spark  Gap. 

Determination  of  the  Approximate  Number  of  Complete  Oscilla- 
tions in  a  Wave  Train  before  the  Amplitude  of  the  Oscilla- 
tions falls  to  0.01  of  the  Maximum. 

Measurement  of  the  Damping  of  a  Coupled  System. 

To  Reduce  the  Logarithmic  Decrement  of  a  Coupled  System 
Found  to  be  Greater  than  the  Legal  Limit. 

Method  of  Procedure  in  the  Adjustment  of  the  Sending  Station 
to  Comply  with  the  Act  to  regulate  Radio  Communication 
Approved  August,  1912. 

Where  the  Wave  Length  is  not  Restricted  by  Law  or  Official 
Order. 

CHAPTER  VI 

MEASUREMENT  or  WAVE  LENGTH  or  THE  RECEIVING  STATION  ...     48 

Calibration  of  a  Receiving  Set  having  a  Double-slide  Tuning  Coil. 

Calibration  of  Inductive  Type  Receiving  Set  having  an  Untuned 
Secondary  and  Variable  Primary. 

Second  Method. 

Calibration  of  an  Inductive  Type  Receiving  Set  with  Variable  Con- 
denser in  Series  or  Parallel,  Secondary  Untuned. 

Calibration  of  Inductive  Type  Receiving  Set  with  Tuned  Secondary. 

Calibration  of  the  Antenna  Circuit. 

Calibration  of  the  Secondary  Circuit. 

Measurement  of  Incoming  Wave  from  a  Distant  Sending  Station. 

CHAPTER  VII 

MEASUREMENT  OF  CAPACITY  AND  INDUCTANCE    .,,......'...     59 

Capacity  of  a  Condenser  by  the  Substitution  Method. 

Capacity  of  a  Condenser  in  an  Oscillatory  Circuit  with  a  Known 

Inductance. 

Measurement  of  the  Capacity  of  the  Antenna. 
Determination  cf  the  Coefficient  of  Self-inductance. 
Measurement  of  the  Coefficient  of  Mutual  Inductance. 
Determination  of  the  Coefficient  of  Coupling. 
Use  of  the  Logarithmic  Chart  for  Calculating  the  Frequency,  Wave 

Length,  Inductance  and  Capacity  of  Oscillatory  Circuits. 
Corrections  for  Values  of  Inductance  or  Capacity  Greater  or  Less 

than  the  Values  given  on  the  Chart. 
INDEX  69 


PRACTICAL    USES    OF    THE    WAVE 
METER  IN  WIRELESS  TELEGRAPHY 

CHAPTER  I 
GENERAL  REMARKS 

A  wave  meter  is  essentially  a  calibrated,  closed  oscillatory 
circuit,  having  inductance  and  capacity,  either  or  both  of  which 
are  variable.  The  resistance  of  such  a  circuit  is  small  in  com- 
parison with  its  inductance.  It  is,  in  reality,  a  small  wireless 
set,  which,  when  used  with  any  one  of  many  forms  of  detector 
usually  supplied  with  it,  can  be  used  as  a  receiving  set,  from 
which  we  can  read  directly  the  wave  length  emitted  by  any  wireless 
sending  circuit,  or  coupled  oscillatory  circuits ;  or,  when  used  with 
proper  means  for  exciting  it,  may  be  used  as  a  miniature  sending 
set,  with  which  we  can  excite,  in  any  nearby  oscillatory  circuit, 
waves  of  any  desired  length  within  the  limits  of  the  wave  meter. 

As  the  operation  of  this  device,  and  the  intelligent  use  of  it 
are  based  upon  a  knowledge  of  the  well-known  principles  of 
resonance,  a  brief  review  of  these,  and  of  some  of  the  preliminary 
principles  of  wireless  telegraphy  may  serve  to  make  the  matter 
clearer  to  some  who  take  it  up  for  the  first  time,  or  who  have  left 
the  theory  far  behind  in  the  practical  operation  of  wireless 
stations. 

DEFINITIONS 

Alternating  Current. — An  alternating  current  is  one  that 
periodically  passes  through  all  values,  flowing  first  in  one  direc- 
tion, then  in  the  other.  This  alternating  current  is  due  to  an 
alternating  e.m.f .  that  gradually  increases  from  zero  to  a  positive 
maximum,  then  decreases  to  zero,  and  then  reverses  its  sign, 
increases  to  a  negative  maximum  and  then  decreases  to  zero. 

Amplitude. — The  greatest  positive  value,  or  greatest  negative 
value  of  the  alternating  current  or  of  potential,  is  called  the 
amplitude. 


t 

2  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

Each  complete  set  of  values  is  called  a  cycle.  Half  a  cycle 
is  called  an  alternation. 

The  time  it  takes  the  current  or  the  potential  to  complete  one 
cycle  or  two  alternations,  is  called  a  period  (T). 

The  number  of  complete  periods  or  cycles  executed  in  a  second 
is  called  the  frequency  (ri). 

A  high-frequency  current  is  one  irl  which  the  frequency  is 
reckoned  in  thousands. 

When  the  frequency  rises  to  any  value  between  a  hundred 
thousand  and  a  million,  electric  oscillations  are  said  to  exist  in 
the  circuit. 

When  an  alternating  current  of  very  high  frequency  and  of 
constant  amplitude  exists  in  a  circuit,  undamped  oscillations 
are  produced. 

Damped  Oscillations.  —  Damped  oscillations  are  those  con- 
sisting of  a  limited  number  of  alternations,  the  amplitude  of 
which  is  continually  decreasing. 

When  damped  oscillations  exist  in  a  circuit  without  spark  gap 
they  decay  in  amplitude  according  to  the  law  that  the  ratio  of 
the  amplitude  of  current  of  any  oscillation  to  that  of  the  next 
succeeding  it  is  constant,  and  this  constant  ratio  is  called  the 
damping  factor  of  the  oscillations.  The  Napierian  logarithm  of 
the  ratio  of  the  amplitude  of  one  oscillation  to  that  of  the  suc- 
ceeding one  is  called  the  logarithmic  decrement,  or  briefly,  the 
decrement. 

A  train  of  oscillations  is  said  to  be  highly  damped  if  the  loga- 
rithmic decrement  is  large;  feebly  damped  if  it  is  small. 

Oscillatory  Circuit.  —  An  oscillatory  circuit  is  one  in  which 
some  form  of  inductance,  and  some  form  of  condenser  are  joined 
in  series,  the  resistance  of  the  circuit  being  small  in  comparison 
with  the  inductance. 

Let  R  =  Resistance  in  ohms  of  the  circuit. 
C  =  Capacity  in  farads. 
L  =  Inductance  in  henrys. 


Then,  if  R  is  greater  than  2*-^  in  a  circuit  through  which  a 

condenser  is  discharged,  no  oscillation  will  take  place  in  the 
circuit,  and  the  circuit  is  called  aperiodic. 


If,  however,  R  is  less  than  2  --^  the  discharge  will  be  oscilla- 
tory, electricity  moving  backward  and  forward  in  the  discharge 


GENERAL  REMARKS  3 

circuit  with  gradually  decreasing  amplitude,  until  the  energy  of 
the  condenser  charge  is  completely  dissipated  by  resistance  and 
radiation. 

For  any  oscillatory  circuit,  then,  it  may  be  shown  that  the 
circuit  vibrates  in  its  natural  period  equal  to 


and  the  frequency  of  the  electric  oscillations  equals 

1  1 


where  T  is  measured  in  seconds,  L  in  henrys,  and  C  in  farads. 

The  above  formulae  are  only  approximate,  but  considered 
sufficiently  accurate  for  practical  purposes. 

The  formula  for  the  frequency  may  be  reduced,  for  conven- 
ience in  calculation,  to  the  following  form : 

5.033  X106 


n  = 


\/C  mfds.XL  cm. 


where  the  inductance,  L,  is  in  absolute  electromagnetic  units, 
that  is,  in  centimeters,  and  (7,  the  capacity,  in  microfarads. 

1  microhenry  =0.000001  henry  =  1000  cm. 

1  microfarad    =0.000001  farad  

Oscillation  Constant. — The  expression  \/CxL  is  sometimes 
called  the  oscillation  constant  of  the  circuit.  In  the  United 
States  it  is  more  common  to  define  the  " oscillation  constant" 
as  simply  the  product  of  the  capacity  times  the  inductance,  and 
further,  in  the  tables  furnished  to  the  Signal  Corps  stations 
equipped  with  the  receiving  sets  of  the  Wireless  Specialty  Appa- 
ratus Co.,  the  " oscillation  constant"  is  given  as  the  product  of 
the  capacity  in  microfarads  and  the  inductance  in  microhenrys. 
Syntonic  Circuits. — When  two  oscillatory  circuits  have  the 
same  time-period,  or  period,  as  it  is  called,  they  are  called 
syntonic  circuits,  and  are  said  to  be  in  resonance  with  each  other. 
This  is  the  case  when  the  oscillation  constants,  or,  without  ex- 
tracting the  square  root,  when  the  product  of  the  capacity  and 
inductance  of  the  two  circuits  is  the  same,  though  the  individual 
values  may  be  very  different.  Thus,  a  circuit  having  an  induct- 
ance of  5000  cm.  and  a  capacity  of  0.005  microfarads  will  have 
the  same  period,  and,  as  we  shall  see  later,  the  same  wave  length, 
as  a  circuit  having  an  inductance  of  25,000  cm.  and  0.001  mfds. 


4  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

If  oscillations  are  set  up  in  a  circuit  having  a  certain  period, 
and,  if  the  period  of  another  oscillatory  circuit  near  it  is  gradually 
changed,  either  by  changing  its  inductance  or  its  capacity,  un- 
til the  period  of  the  latter  circuit  is  made  the  same  as  that  of 
the  first,  a  current-indicating  device  in  the  second  circuit  will 
give  evidence  of  a  considerable  increase  of  current  in  this  cir- 
cuit as  it  approaches  the  resonance  condition,  and  of  a  decrease 
of  the  current,  the  further  the  period  of  the  second  circuit 
recedes  from  that  of  the  exciting  circuit. 

If  this  second  oscillatory  circuit,  containing  the  current- 
indicating  device,  is  provided  with  a  scale  for  directly  reading 
therefrom  the  period  of  the  circuit  for  any  given  value  of.  its 
variable  inductance  or  variable  capacity,  we  may  say  that  the 
period  of  the  exciting  circuit  is  the  same  as  that  read  from  the 
scale  or  taken  from  the  calibration  curve  of  the  second  circuit. 

Operation  of  the  Wave  Meter.  —  This  is  the  principle  of  opera- 
tion of  the  wave  meter,  and  the  operation  of  bringing  one  oscilla- 
tory circuit  into  resonance  with  another  is  called  tuning. 

The  relation  between  the  wave  length,  X,  the  velocity  of  prop- 
agation of  the  wave  (F),  and  the  period  (T)  of  an  oscillatory 
system  is  given  by  the  equation 

V  =  ~  or,  T=± 

and,  since  n=-^ 

y 

.  then,  V  =  nX  or,  \  =  — 

that  is,  the  wave  length  in  meters  is  equal  to  the  velocity  of  the 
wave  in  meters  per  second  divided  by  the  frequency  in  cycles 
per  second, 

where  V  is  taken  as  300,000,000  meters  per  second, 
X  the  wave  length  in  meters, 

and  n  the  frequency. 

The  expression  for  the  wave  length  in  meters, 


n 
may  be  reduced  to  the  very  convenient  practical  form, 


meters  =  59.6V  C  mfds.   X  L  cm. 


GENERAL  REMARKS  5 

in  which  form  it  may  be  used  for  the  purpose  of  calculating  the 
values  of  capacities  or  inductances,  as  will  be  described  later. 

Wave  meters  are  usually  calibrated  to  read  directly  in  meters; 
and,  the  wave  length  of  a  circuit  being  known,  its  period  or  its 
frequency  can  easily  be  calculated  from  the  formulae  given  above. 

Wave  Meter  Circuits.— These  are  all  reducible  to  the  elemen- 
tary form  shown  in  Fig.  1,  which  represents  a  closed  oscillatory 
circuit  having  a  fixed  inductance,  L,  and  a  variable  condenser, 
C,  though  most  wave  meters  are  supplied  with  several  fixed 
inductances,  which  are  easily  substituted  for  one*  another  in 
the  wave  meter  circuit.  These  enable  the  wave  meter  to  have 
a  range,  usually  from  about  150  to  6000  meters,  in  the  various 
types  seen  at  present. 

The  Wave  Meter  as  a  Receiving  Device.— For  the  purpose  of 


FIG.  1. 


FiG/2. 


Spark 
Gap 


1 

0 

ex 

"T 

2r                   <=> 

r 

-u                       o{ 

0 

o 

H.W. 

FIG.  3.  FIG.  4. 

FIGS.  1  to  4. — Wave  meter  attachments. 


measuring  the  wave  lengths  of  sending  sets,  the  wave  meter  is 
usually  provided  with  one  or  more  of  the  following  forms  of 
energy-indicating  devices  shown  in  Figs.  2,  3,  4,  5,  6,  7,  8,  9, 
and  10: 

1.  A  small  tube  (Fig.  2)  containing  helium  or  neon  gas  is  con- 
nected across  the  terminals  of  the  variable  condenser,  C,  and  glows 
when  the  resonance  condition  is  reached. 

2.  A  very  minute  spark  gap  (Fig.  3)  placed  across  the  variable 
condenser  will  spark  when  resonance  is  obtained.     This  is  some- 
times added  to  wave  meters  using  a  helium  tube  to  prevent 
burning  out  the  tube,  and  sparking  in  the  variable  condenser 
itself. 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


3.  A  hot-wire  ammeter  (Fig.  4),  calibrated  to  register  from  0 
to  100  milliamperes,  or  a  thermo-ammeter,  such  as  a  Duddell,  of . 
very  low  resistance,  with  about  the  same  scale  limits,  can  be 
inserted  directly  into  the  wave  meter  circuit,  and  is  the  most 
accurate  and  useful  indicating  device,  since  it  not  only  indicates 
the  exact  point  of  resonance,  but  enables  us  to  plot  resonance 
curves  showing  the  amount  of  current  in  the  wave  meter  circuit, 
not  only  at  the  resonance  position,  but  also  as  the  wave  meter 
departs  from,  or  approaches,  exact  syntony.  In  practice,  most 
well  designed  wave  meters  have  such  hot  wire  instruments  either 


Thermoelement 
(^Galvanometer 

FIG.  5. 


FIG.  6. 


Crystal  Oct. 


O 
O 

1L 

O 
O 


FIG.  7.  FIG.  8. 

FIGS.  5  to  8. — Wave  meter  attachments  for  measuring  the  sending  apparatus. 

inductively  connected  or  provided  with  a  low  resistance  shunt. 
(Fig.  25.)     The  instrument  is  usually  a  hot-wire  wattmeter. 

4.  A  thermo-element  (Fig.  5)  of  low  resistance,  constructed  as 
described  later  (see  Fig.  26  and  accompanying  text),  is  inserted 
in  the  wave  meter  circuit,  and  shunts  a  low  resistance  galvan- 
ometer. The  readings  of  the  galvanometer  are  proportional  to 
the  square  of  the  oscillatory  current  through  the  junction,  and, 
as  the  galvanometer  and  the  thermo-element  can  be  calibrated 
for  alternating  currents  by  comparison  with  a  hot-wire  ammeter, 
this  form  of  indicating  device  may  be  used  not  only  to  indicate 
resonance,  but,  by  its  use,  resonance  curves  may  be  plotted  as 
with  the  hot-wire  ammeter,  and  the  damping  of  any  circuit 


GENERAL  REMARKS  7 

determined  as  shown  later.  In  using  this  device  it  may  be  found 
advisable  to  introduce  some  inductance  in  the  galvanometer 
leads. 

5.  If  the  variable  condenser  of  the  wave  meter  (Fig.  6)  is 
shunted  by  a  circuit  containing  a  detector  of  the  crystal  type, 
such  as  carborundum,  the  sensibility  of  which  is  not  affected  by 
nearby  sending  apparatus,  in  series  with  a  high  resistance  tele- 
phone receiver,  T,  the  maximum  loudness  of  the  sound  heard 
in  the  telephone  receiver  will  indicate  when  the  wave  meter  is 
in  resonance  with  the  sending  circuit  to  which  it  is  being  tuned. 
This  is  the  detecting  device  supplied  with  the  Marconi  wave 
meter,  and  with  one  type  of  Telefunken  instrument. 

Professor  George  W.  Pierce  is  of  the  opinion  that,  due  to  the 
possibility  of  the  detector  affecting  the  period  of  the  meter,  it 
is  better,  or  at  least  simpler,  to  connect  the  detector  unilaterally, 
as  shown  in  Fig.  7,  and  shunt  the  receivers  about  it.  This  in- 
dicating device  can  always  be  improvised  at  any  station,  and 
applied  to  any  wave  meter.  It  is  especially  recommended  for 
measurement  of  the  natural  wave  length  of  the  antenna.  Any 
detector  will  do,  but  iron  pyrites  or  carborundum  is  recommended. 

6.  A  dynamometer  telephone  (Fig.  8),  consisting  of  a  small 
coil  of  wire  wound  on  a  small,  hard  rubber  bobbin,  and  placed 
near  a  diaphragm  of  copper  or  silver,  will,  due  to  the  reaction 
between  the  coil  and  the  disc,  when  an  oscillatory  current  is 
sent  through  the  coil,  indicate  the  resonance  point  by  the  maxi- 
mum loudness  of  the  sound  heard  in  the  telephone.     The  coil 
of  wire  in  the  dynamometer  telephone,  being  an  inductance, 
must  be  in  the  wave  meter  circuit,  when  the  latter  is  being  cali- 
brated, or  if  removed  for  the  purpose  of  introducing  some  other 
device,  as  seen  later  (Fig.  13  and  accompanying  explanation),  a 
coil  of  wire  having  exactly  similar  inductance  must  be  inserted 
in  the  circuit,  in  order  that  the  readings  of  the  wave  meter  may 
be  correct. 

This  is  the  form  of  receiving  device  furnished  with  the  Pierce 
wave  meter. 

7.  An  aperiodic  circuit,  A  (Fig.  9),  consisting  of  an  inductance, 
a  detector  of  the  carborundum,  iron  pyrite,  or  silicon  steel-wire 
type,  and  a  small  stopping  condenser  of  about  0.003  mfd.  capacity 
shunted  by  a  pair  of  wireless  telephone  receivers,  if  loosely  coupled 
with  the  wave  meter  inductance,  will  indicate,  by  the  loudness 
of  the  sound  in  the  telephone  receivers,  when  the  wave  meter 


8 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


is  in  r  esonance  with  the  sending  circuit.  Needless  to  say,  the 
detector  must  be  in  a  sensitive  adjustment  to  permit  of  the 
loosest  coupling  between  the  coils  of  the  aperiodic  circuit  and 
the  receptor  loop  of  the  wave  meter. 

8.  The  telephone  receiver  of  the  aperiodic  circuit  may  be  re- 
placed by  a  galvanometer  as  shown  in  Fig.  10.  Quantitative 
measurements  of  currents  in  the  circuit,  which  afford  a  better 
approximation  of  the  exact  point  of  resonance,  may  then  be  made 
by  this  means,  and  resonance  curves  plotted,  if  desired,  if  care 
be  taken  to  preserve  the  coupling  of  the  wave  meter,  aperiodic 
circuit,  and  circuit  to  be  measured,  unchanged  throughout  the 
series  of  measurements  resulting  in  a  curve. 


Tel. 


I — MK- j 

Gal.<gCJ=         A          I 


FIG.  9. 


FIG.  10. 


FIG.  11.  FIG.  12. 

FIGS.  9  to  12. — Wave  meter  attachments,  receiving  and  sending. 

The  deflections  of  the  galvanometer  are  to  each  other  as  the 
square  of  the  current  passing  through  it,  and,  if  the  galvanom- 
eter shunting  the  detector  has  been  previously  calibrated,  by 
comparison  with  a  known  standard,  the  currents  passing  through 
the  galvanometer  may  be  read  directly  from  the  calibration 
curve  previously  prepared. 

The  Wave  Meter  as  a  Sending  Set. — For  the  purpose  of 
measuring  the  wave  length  of  any  given  adjustment  of  the  receiv- 
ing apparatus  of  a  station,  or,  in  any  other  measurement,  where 
it  is  necessary  to  send  out  waves  of  definite  length  by  means  of 
a  wave  meter,  it  is  necessary  to  charge  the  variable  air  condenser 
of  the  wave  meter  continuously  from  some  source  and  have  it 
discharge  through  the  inductance  of  the  wave  meter. 


GENERAL  REMARKS 

The  simplest  and  most  efficient  way  of  doing  this  is  indicated 
in  Fig.  11,  where  the  condenser  is  excited  by  the  "whipcrack" 
method. 

A  circuit  consisting  of  a  buzzer,  B,  in  series  with  a  couple  of 
cells  of  dry-battery,  and  a  key  or  switch,  is  tied  to  the  terminals 
of  the  variable  condenser  of  the  wave  meter.  When  the  key  is 
depressed,  or  the  switch  closed,  the  current  through  the  induct- 
ance, L,  of  the  wave  meter  has  energy  %LI2,  and  when  the  buzzer 
circuit  breaks,  this  energy  oscillates  between  the  condenser  and 
the  inductance  of  the  wave  meter,  and 
sets  up  oscillations  in  any  oscillatory  cir- 
cuit to  which  the  wave  meter  may  be 
coupled. 

The  wave  length  emitted  by  the  wave 
meter  is  that  indicated  by  the  condenser 
pointer  passing  over  the  scale  of  wave 
lengths. 

A  small  medical  shocking  coil  is  a  con- 

.      ,    .  .  ,  r*    .  ,  „  FIG.    13. — Wave  meter 

vement  form  of  buzzer  to  be  inserted  for    uging  induction   coil  and 

the  purpose  mentioned,  the  primary  alone    spark  gap  for  excitation. 

being  used.     It  is  to  be  noted  that  the 

buzzer  circuit  is  completed  through  the  inductance  of  the  wave 

meter. 

Another  form  of  buzzer-excited  circuit  is  that  shown  in  Fig.  12. 

The  buzzer  used  in  this  circuit  is  an  ordinary  Signal  Corps 
Field  Buzzer,  Model  1905.  Across  the  make-and-break  of  the 
buzzer,  the  condenser  of  the  wave  meter  is  shunted.  It  is, 
however,  necessary  to  have  a  non-inductive  resistance,  R,  in 
series  as  shown  in  the  diagram.  This  buzzer  gives  a  high,  even 
note,  which  is  very  satisfactory  for  use  with  the  wave  meter  as  a 
sending  device. 

A  third  form  of  attachment  to  make  the  wave  meter  a  sending 
set  is  that  shown  in  Fig.  13.  This  is  the  form  of  sending  device 
furnished  with  the  Pierce  wave  meter.  A  miniature  spark  gap, 
G,  is  inserted  in  the  wave  meter  circuit,  and  a  small  induction 
coil  giving  anywhere  from  a  quarter  to  a  one-inch  spark,  operated 
on  a  couple  of  cells  of  battery,  is  used  to  charge  the  wave  meter 
condenser;  the  secondary  of  the  spark  coil  being  attached  to 
the  spark  gap  as  shown.  As  the  plates  of  the  condenser,  C,  are 
usually  very  close  together,  sparking  will  take  place  in  the  con- 
denser, unless  the  spark  gap  is  reduced  to  the  smallest  possible 


10  -WAVE  METER  IN  WIRELESS  TELEGRAPHY 

width.  From  0.2  to  0.1  mm.  is  the  ordinary  width  of  gap  used. 
As  the  Pierce  wave  meter  uses  the  dynamometer  telephone  as  a 
receiving  device,  the  inductance  of  the  dynamometer  telephone 
which  is  removed  when  the  spark  gap  is  inserted,  is  replaced  by 
a  coil  in  the  base  of  the  spark  gap,  which  has  the  same  inductance 
as  the  telephone. 


CHAPTER  II 


TYPES  OF  WAVE  METERS  IN  USE  IN  THE  U.  S. 
SIGNAL  CORPS 

The  Pierce  Wave  Meter. — A  diagram  of  the  connections  of 
this  meter  is  shown  in  Fig.  14. 

Ordinarily  no  indicating  device  other  than  the  dynamometer 
telephone  is  supplied  with  this  wave  meter,  though  a  helium 
tube  may  be  used  with  it. 

This  telephone  is  to  be  attached  to  the  binding  posts,  which 
are  near  together  to  the  left 


Receptor  Loop 


Helium 
Tube 


L' 


Dynamometer  Telephone 

FIG.  14. — Pierce  wave  meter  connections. 


of  the  wave  meter  scale.  If 
it  be  desired  to  attach  a 
helium  tube,  the  telephone 
should  be  left  in  circuit,  and 
the  helium  tube  is  shunted 
around  the  condenser  by  two 
leads  which  are  attached,  one 
to  the  left  hand  binding  post 
of  the  two  used  for  the  tele- 
phone receivers,  and  the  other 
to  the  idle  binding  post  at  the 
back  of  the  instrument. 

The  smaller  inductance,  L' 

(receptor  loop),  is  wound  on  a  hard  rubber  ring  which  is  pivoted 
at  the  back  of  the  instrument,  so  as  to  permit  it  to  be  revolved 
into  any  desired  position.  Another  inductance,  L",  of  many 
turns,  is  placed  in  the  base  of  the  wave  meter,  and  is  used  for 
the  purpose  of  increasing  the  wave  length  of  the  circuit,  when 
measuring  long  waves. 

A  three-point  switch  at  the  right  of  the  instrument,  marked 
L  and  S,  cuts  in  either  all  or  only  part  of  the  inductance  as  de- 
sired. For  waves  up  to  700  m.  put  the  switch  on  S  (short 
waves),  and  read  the  wave  length  in  meters  from  the  position 
of  the  pointer  over  the  red  scale.  This  scale  reads  as  low  as 
150m. 

11 


12  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

The  position  of  the  pointer  for  maximum  sound  in  the  tele- 
phone is  the  wave  length  in  meters.  If  the  switch  is  on  L  (long 
waves),  the  black  scale  should  be  read  and  the  wave  lengths  in 
meters  obtained  from  it.  The  range  of  the  black  scale  is  be- 
tween 500  and  2320  meters. 

In  case  the  sounds  in  the  telephone  receiver  are  too  loud  for 
accurate  determinations,  their  intensity  may  be  reduced,  either 
by  moving  the  wave  meter  farther  from  the  exciting  circuit 
or,  more  conveniently,  by  turning  the  receptor  loop,  so  that 
the  inductive  action  is  diminished.  In  the  final  setting  it  is 
desirable  to  have  the  sound  in  the  telephone  just  audible  at 
resonance. 

Caution. — The  makers  caution  users  of  this  instrument  not 
to  attempt  to  open  the  telephone  receiver,  and  not  to  change  or 
break  the  leads  of  the  telephone,  as  injury  to  the  telephone  will 
disturb  the  calibration. 

In  stowing  away  the  apparatus  the  pointer  should  be  left  free 
from  obstructions.  To  this  end,  whenever  the  instrument  is  to 
be  transported,  it  is  advisable  to  disconnect  the  telephone  and 
place  it  in  the  clamp  in  the  cover  of  the  box,  with  the  leads 
secured  under  the  wooden  buttons.  The  receptor  loop  should 
be  folded  in  with  knob  upward,  so  that  the  pointer  can  be  rotated 
under  the  loop  without  interference.  In  packing  for  shipment, 
put  a  pad  of  felt  on  top  of  the  handle,  inside  the  box  so  that  the 
condenser  cannot  rotate. 

Telefunken  Wave  Meter  Type  E.  KI.  W.— This  wave  meter 
was  supplied  several  years  ago  with  the  first  2  kw.  wagon  set, 
but  in  the  more  recent  sets  has  been  superseded  by  the  Type 
E.  Ki.  Wk.  meter  described  later  in  this  pamphlet. 

For  diagrams  of  connections,  see  Figs.  2  and  11. 

The  cover  of  the  E.  Ki.  W.  meter  can  be  removed  to  facili- 
tate the  turning  of  the  folding  handle  of  the  condenser. 

Supplied  with  the  instruments  are  the  following  parts : 

A  variable  capacity  with  pointer  moving  over  scale  from  0° 
to  90°. 

Buzzer  giving  approximately  500-cycle  note,  with  switch 
which  can  be  closed  to  give  continuous  buzz,  or  used  as  sending 
key,  if  desired  to  send  regular  telegraphic  signals.  This  feature 
will  be  referred  to  again  later. 

Four  flat  inductance  coils,  readily  interchangeable,  giving 
the  wave  meter  a  range  from  about  300  to  3450  meters: 


WAVE  METERS  IN  USE  IN  THE  U.  S.  SIGNAL  CORPS     13 

Coil  I  -  304  to  732  m. 
Coil  II  --  657  to  1568m. 
Coil  III— 1425  to  2720  m. 
Coil  IV —2372  to  3446m. 

Parallel  leads  with  plug  contacts  for  connecting  flat  inductance 
coils  to  variable  condenser. 

Helium  tube  which  can  be  placed  across  terminals  of  variable 
condenser  by  spring  clips  attached  thereto.  Two  helium  tubes 
are  supplied  with  each  instrument.  Care  must  be  taken  to  pre- 
vent protuding  sealed  end  of  glass  tube  from  being  broken  off, 
and  thus  permitting  gas  to  escape  from  tube. 

Aperiodic  circuit  (see  Fig.  15,  and  A,  Fig.  9),  supplied  with 


FIG.  15. — Aperiodic  circuit. 

this  wave  meter  consists  of  a  flat  plate,  H,  of  hard  rubber,  in  the 
base  of  which  is  a  flat  spiral  of  wire,  B,  connected  as  shown  with 
a  small  fixed  mica  condenser,  capacity  about  0.015  mfd.  and 
spring  clips,  C,  C',  for  the  insertion  of  one  of  the  detectors  regu- 
larly supplied  with  the  wagon  set.  Binding  posts  are  provided 
for  the  purpose  of  attaching  the  telephone  receiver  to  fixed 
condenser  terminals. 

The  four  flat  inductance  coils  of  the  wave  meter  are  carried 
in  the  lower  part  of  the  wave  meter  case,  and  should  be  placed 
in  their  proper  compartments  to  facilitate  ready  removal.  The 
parallel  leads  are  to  be  carefully  coiled  up  and  placed  in  the  large 
compartment,  partially  occupied  by  the  variable  condenser  and 
buzzer.  The  condenser  pointer  must  always  be  placed  at  the 
90°  mark,  before  any  attempt  is  made  to  place  this  coil  of  wire 


14 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


in  the  same  compartment,  if  injury  to  the  condenser  is  to  be 
prevented. 

There  is  only  one  adjustment  for  the  buzzer,  and  to  regulate 
this  the  screw  head  immediately  to  the  upper  left  of  the  buzzer 
switch  must  be  turned  with  a  screw-driver  while  the  buzzer  key 
is  depressed.  The  buzzer  is  properly  adjusted  when  it  gives  a 
clear  singing  note,  in  response  to  taps  on  the  buzzer  key.  It 
will  be  noticed  that  re-adjustment  of  the  buzzer  will  probably 
have  to  be  made  on  attaching  the  largest  of  the  inductance  coils 
to  the  wave  meter. 

The  scale  over  which  the  pointer  moves  is  graduated  only  in 
degrees. 

Upon  each  flat  coil  is  marked  in  white  letters  the  wave  lengths 
corresponding  to  every  ten  degrees  of  condenser  setting,  thus : 


Coil  II 


C  =  10°|20° 

30° 

40° 

50°  [  60° 

70° 

80° 

90° 

J=  657(818 

965 

1098 

12151316 

1409 

1492 

1568 

|16.1|14.7 

13.3|11.7|10.1 

9.3 

8.3 

7.6 

The  figures  in  red  on  the  line  below  those  in  white  are  the  in- 
crements per  degree  of  scale  reading,  which  are  used  as  follows : 

Suppose  we  find  that  we  get  resonance  when  using  plate  No.  2, 
and  the  condenser  reading  for  resonance  is  30°.  This  we  can 
read  directly  from  the  scale  as  965  meters.  Suppose,  however, 
that  we  get  resonance  at  42f°,  instead  of  30°.  We  see  from  the 
table  that  for  40°  we  get  1098  meters.  The  red  figures  on  the 
line  below,  between  40°  and  50°,  reading  11.7,  indicate  that  for 
every  scale  division,  above  40°,  we  must  add  11.7  meters  to  the 
40°  reading,  to  get  the  correct  reading  of  the  wave  length  in 
meters;  so,  by  multiplying  2f°  by  11.7,  we  get  32  meters,  which 
is  to  be  added  to  the  40°  reading.  Hence,  the  wave  length  is 
1130  meters. 

On  the  other  hand,  if  it  is  desired  to  excite  in  a  nearby  receiving 
set  by  means  of  the  wave  meter,  a  wave  of  given  length,  say 
1000  meters,  we  will  have  to  go  through  the  following  process  to 
find  what  coil  is  to  be  used,  and  at  what  condenser  reading  the 
pointer  must  be  set  in  order  to  send  out  the  1000  meter  wave. 

An  inspection  of  the  plates  will  show  which  coil  has  1000  meters 
within  its  limits.  Thus,  we  find  that  with  coil  No.  2,  30°  gives 
965  meters,  and  40°  gives  1098  meters.  1000  meters  lies  some- 
where between  30°  and  40°,  so  coil  No.  2  is  to  be  used. 

Subtract  the  nearest  lower-numbered  white  figures  on  the  plate 


WAVE  METERS  IN  USE  IN  THE  U.  S.  SIGNAL  CORPS     15 

from  the  desired  wave  length,  in  this  case  1000  —  965  =  35,  and 
divide  this  quotient  by  the  red  figures  between  the  30°  and  40° 
wave  lengths.  35-^13.3  =  2.6°,  and  we  thus  find  that  2.6°  are 
to  be  added  to  30°,  making  a  total  of  32.6°,  in  order  that  the 
condenser  pointer  may  be  properly  set,  so  that  the  wave  meter 
may  send  out  the  1000  meter  wave. 

For  greatest  accuracy,  the  readings  of  the  pointer  should  be 
estimated  to  the  nearest  tenth  of  a  degree. 

The  above  is,  perhaps,  not  as  convenient  a  process  as  reading 
the  wave  length  directly  from  the  condenser  scale,  but  the  ac- 
curacy of  this  wave  meter  cannot  be  questioned,  and  the  little 
extra  labor  used  in  calculation  is  well  repaid  by  the  accuracy  of 
the  results  obtained.  Considerable  trouble  and  labor  will  be 
obviated,  if,  from  the  data  given  on  the  plates,  calibration  curves 
of  wave  lengths  against  degrees  of  condenser  scale  are  plotted. 

The  Type  E.  Ki.  Wk.  Meter. — This  is  the  type  of  wave  meter 
issued  at  the  present  time  with  each  Telefunken  wagon  set,  for 
field  use.  A  top  view  of  this  wave  meter  is  shown  in  Fig.  16. 

Four  different  inductances,  any  one  of  which  can  be  brought  in 
circuit  with  the  variable  air  condenser  by  revolving  the  knob, 
K,  are  placed  near  the  back  wall  of  the  box,  F,  where  they  are 
in  inductive  relation  with  the  coupling  coil,  which  is  inserted  in 
the  groove  G,  shown  at  the  back  of  the  box.  This  coupling  coil 
is  connected  to  another  similar  coil  of  wire  by  long,  parallel 
leads,  to  permit  this  latter  coil  to  be  brought  near  the  circuit 
to  be  measured.  The  closeness  of  coupling  between  the  inter- 
mediate, or  coupling  circuit,  and  the  coils  of  the  wave  meter 
within  the  box  may  be  varied  by  sliding  the  coupling  coil  along 
the  groove  G.  The  reaction  of  the  coupling  coil  on  the  wave 
meter  is  practically  nil,  so  that  the  correctness  of  the  readings 
of  the  wave  length  is  assured. 

The  indicating  arm  A,  carrying  an  index,  moves  over  the  four 
different  scales  corresponding  to  the  different  inductances.  At 
the  little  window,  W,  is  seen  in  Roman  numbers,  on  a  colored 
ground,  the  number  of  the  coil  being  used.  The  four  arcs 
marked  7,  //,  ///,  and  IV,  bearing  the  graduations  in  wave 
lengths  corresponding  to  any  position  of  arm  A,  are  colored  to 
correspond  to  the  colors  shown  at  W.  Thus,  the  red  field 
bearing  the  figures  II,  seen  at  W,  indicates  that  we  are  to  read  the 
red,  or  second  scale  of  wave  lengths;  the  blue  field,  the  fourth 
scale,  etc. 


16 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


The  scales  range  as  follows: 
I.  White  scale— 300  to  600  meters. 
II.  Red  scale— 500  to  1058  meters. 

III.  Yellow  scale— 1000  to  1950  meters. 

IV.  Blue  scale— 1600  to  3250  meters. 

The  wave  lengths  are  read  directly  off  the  scale. 
Attached  to  arm  A ,  and  making  an  angle  of  90°  with  it,  is  the 
pointer  P,  which  moves  over  a  scale  of  degrees  from  0°  to  90°, 


FIG.  16. — Type  E.  K.  I.  Wk.  wavemeter. 

which  may  be  read  if  the  wave  lengths  are  taken  from  a  curve, 
instead  of  read  from  wave  length  scales  under  arm  A. 

The  connections  are  practically  similar,  with  the  exception 
of  the  multipolar  combination  switch  wiring,  to  the  connections 
of  the  type  E.  Ki.  W.  meter  before  described.  The  buzzer,  B, 
is  outside  of  the  box  and  connects  to  the  dry-battery  inside  by 
the  plug  connections  underneath  it. 

Care  must  be  exercised  in  adjustment  of  this  buzzer,  for  the 
platinum  cross-wires,  which  form  the  make  and  break  contacts, 
may  be  broken  by  screwing  too  tightly  together.  There  are  two 


WAVE  METERS  IN  USE  IN  THE  U.  S.  SIGNAL  CORPS     17 

milled  adjusting  heads,  one  of  which,  seen  at  X,  and  marked 
Ab—An,  adjusts  the  position  of  one  contact  with  reference  to 
the  other,  and  the  other  at  F,  which  adjusts  the  tension,  causing 
the  note  of  the  buzzer  to  be  raised  or  lowered. 

When  changing  to  the  fourth  coil  from  any  of  the  others,  it 
will  probably  be  necessary  to  re-adjust  the  buzzer,  since  the  higher 
resistance  of  this  coil  will  decrease  the  direct  current  by  which 
the  buzzer  operates.  A  high,  singing  note  is  best  for  purposes  of 
measurement  of  the  receiving  circuit. 

The  usual  small  helium  tube  is  attached  to  the  condenser 
terminals  at  S.  This  is  protected  from  heavy  currents  by  a 
minute  spark  gap,  G. 

For  very  heavy  currents,  a  small  incandescent  lamp,  L,  is 
placed  in  the  wave  meter  circuit,  but  will  rarely  glow.  The 
caution  about  breaking  helium  tubes  supplied  by  the  Telefunken 
Company  applies  to  those  with  this  meter.  They  should 
normally  be  carried  in  cotton  in  a  small  box,  instead  of  in  the 
spring  clips  S. 

The  switch,  R,  when  over  point  M ,  can  be  used  as  a  key  to 
send  Morse  signals,  though,  when  placed  on  point  N,  it  will 
cause  the  buzzer  to  work  continuously,  as  is  normally  done 
when  measuring. 

An  aperiodic  circuit,  similar  to  that  shown  in  Fig.  15,  is 
furnished  for  use  with  this  wave  meter  as  a  detecting  device. 
One  of  the  detectors  belonging  to  the  wagon  set  should  be  used 
with  this  aperiodic  circuit. 

Large  Telefunken  Wave  Meter  Type  E.  G.  W.— This  wave 
meter  has  a  number  of  refinements  not  ordinarily  supplied  with 
wave  meters.  It  has  a  large  range  of  wave  lengths,  100  m. 
to  6000  in.  and  has  a  hot-wire  wattmeter,  in  addition  to 
helium  tubes,  and  detector  and  telephone  receiver,  as  an  indi- 
cator of  current.  The  hot-wire  wattmeter  is  inductively  con- 
nected to  the  principal  inductance,  and  thus,  only  a  small 
fraction  of  the  wave  meter's  energy  is  transferred  to  it.  The 
principle  of  the  circuits  and  connection  of  attachments  are,  with 
a  few  minor  changes,  seen,  in  Fig.  17,  to  be  practically  the  same 
as  in  the  two  wave  meters  previously  described.  A  double 
pointer  on  the  variable  condenser  makes  it  possible  to  read  on 
one  scale  the  number  of  degrees  corresponding  to  resonance,  and 
to  determine  from  an  attached  table,  the  wave  length  corres- 
ponding thereto.  The  other  half  of  the  pointer  indicates  a  point 


18 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


on  a  scale  seen  opposite  an  index  on  the  arm.  This  second  scale 
gives  directly  the  wave  length  in  meters  for  waves  between  400  and 
3400  meters.  This  latter  scale  is  chiefly  for  rough  determina- 
tion. A  curve  table  is  used  whenever  the  exact  determination 
of  a  wave  length  is  desired. 

In  the  figure,  L  is  the  changeable  inductance,  A  the  connect- 
ing wire,  C  the  variable  condenser,  M  that  part  of  the  coil  with 
•  which  the  hot-wire  instrument  is 

coupled,  S  the  buzzer,  B  a  switch 
by  which  the  buzzer,  or  the  dif- 
ferent other  instruments  for 
showing  resonance,  may  be  in- 
serted in  circuit. 

The  condenser  is  a  plate  con- 
denser, contained  in  a  receptacle 
filled  with  oil.  Its  range  is  from 
200  tp  5000  cm. 

F  is  a  safety  spark  gap  around 
the  condenser. 

The  inductance  coils  are  six  in 
number.     Upon  the  back  of  each 
coil  are  shown  the  wave  lengths 
falling  within  range  of  the  coil. 
Contact  between  the  coils  and 
the  handle  is  properly  made  only 
when  the  white  marks  on  them 
are  opposite  one  another. 
The  several  coils,  used  in  connection  with  the  condenser,  be- 
tween 20°   and   170°  give   approximately  the  following    wave 
lengths: 

Coil  I  90  to    260  m. 

Coil  II  -  -  180  to  500  m. 
Coil  III—  400  to  1050  m. 
Coil  IV—  650  to  1800m. 
Coil  V  —1200  to  3400  m. 
Coil  VI  —2100  to  5700  m. 

The  hot-wire  wattmeter,  W,  indicates  the  energy  received  by 
the  wave  meter.  It  is  so  loosely  coupled  with  a  few  turns  of 
the  coil,  L,  that  the  energy  drawn  by  the  wave  meter  from  the 
oscillatory  circuit  is  extremely  small,  and  the  damping  caused 


FIG. 


17. — Large  Telefunken  wave 
meter,  Type  E.  G.  W.     . 


WAVE  METERS  IN  USE  IN  THE  U.  S.  SIGNAL  CORPS     19 

by  the  different  coils  is  very  small  and  nearly  constant.  The 
knob  reaching  through  an  opening  in  the  glass  window  is  used  to 
bring  the  pointer  to  the  zero  of  the  scale. 

To  use  the  hot-wire  instrument,  the  switch,  B,  is  set  on  the 
first  contact. 

Instead  of  the  wattmeter,  either  the  helium  tube,  or  the  tele- 
phone and  detector  may  be  used,  if  it  is  a  question  of  qualitative 
measurement.  For  measuring  wave  lengths,  one  has  the  choice 
of  all  three  devices,  but  for  measurements  of  damping,  the  hot- 
wire wattmeter  must  be  used,  and  it  is  to  be  noted  that  in  all 
cases  where  the  wave  meter  with  its  hot-wire  wattmeter  is  used 
to  obtain  the  logarithmic  decrement,  the  readings  of  this  instru- 
ment should  not  be  squared  as  the  readings  are  themselves  the 
squares  of  the  currents. 

The  helium  tube,  H,  is  connected  directly  to  the  terminals 
of  the  condenser,  C,  and  in  parallel  with  it.  To  use  it,  the  tube 
is  clamped  in  the  holder  provided  for  it.  It  is  to  be  observed 
that  the  ammeter  and  detector  are  first  to  be  taken  out  of  cir- 
cuit, and  the  switch,  B,  set  on  the  first  contact.  The  detector, 
D,  and  the  telephone,  T,  are  in  series  with  each  other,  and  in 
parallel  with  the  condenser  C.  In  using  them  the  switch,  B} 
must  be  set  on  the  fourth  contact. 

The  buzzer,  S,  with  its  accessories,  is  connected  directly  to 
terminals  of  the  condenser,  and  in  parallel  with  it.  In  using  it, 
the  switch,  B,  is  set  on  the  fourth  contact.  If  Morse  signals 
are  used,  the  second  contact  is  to  be  used. 

As  an  accessory,  there  is  furnished  a  support  made  of  pliable 
leather,  with  a  foot-plate  and  clamps  upon  which  the  inductance 
coil  may  be  fastened  in  any  desired  position  with  relation  to  the 
circuit  being  measured. 


CHAPTER  III 

USES  OF  WAVE  METERS 

MEASUREMENT  OF  WAVE  LENGTHS 

The  Wave  Meter  Used  as  a  Receiving  Set 

General. — The  receptor  loop,  or  inductance,  of  whatever 
form  of  wave  meter  is  used,  is,  in  general,  brought  in  the  vicinity 
of  the  inductance  of  the  circuit  being  investigated  and  so  that 
the  lines  of  force  thread  through  both  inductances,  the  coil 
being  held  in  the  hand,  or  placed  on  its  stand,  if  one  is  provided, 
so  as  to  be  conveniently  movable  with  respect  to  the  circuit 
to  be  measured.  The  most  favorable  position  for  the  receptor 
coil  of  the  wave  meter  must  be  determined  by  experiment.  The 
convenience  of  the  long  flexible  connection  between  the  receptor 
coil  of  the  Telefunken  wave  meters  and  box  containing  the  con- 
denser will  be  appreciated  by  those  who  attempt  to  measure  the 
wave  length  of  stations,  where  the  helix  is  attached  to  the  ceil- 
ing. The  difficulty  of  holding  the  Pierce  wave  meter,  the  recep- 
tor loop  of  which  is  directly  attached  to  the  box  containing  the 
condenser,  in  the  vicinity  of  a  helix  so  placed,  and  operating  the 
wave  meter  at  the  same  time,  will  be  appreciated  by  those  who 
try  it.  If,  however,  a  detector  and  telephone  receiver,  connected 
unilaterally  (Fig.  7),  be  used  as  the  current-indicating  device, 
no  difficulty  will  be  experienced,  since  the  meter  can  then  be  used 
yards  away  from  the  circuit  being  measured. 

Using  hot-wire  ammeter,  or  thermo-element  and  galvan- 
ometer (see  Figs.  4  and  5)  as  a  detector,  the  reading  of  the  ammeter 
or  galvanometer  will  increase  until  the  correct  position  of  the 
pointer  over  the  scale  of  wave  lengths,  together  with  the  proper 
inductance  coil,  has  been  ascertained.  The  reading  will  increase 
to  a  maximum,  and  then  become  noticeably  smaller  again. 
Resonance  corresponds  to  the  highest  reading  of  the  instrument. 
The  wave  length  corresponding  thereto  is  read  directly  from  the 
wave  meter,  calculated  from  tables,  or  read  directly  from  curves 
of  wave  lengths  provided  with  the  instrument. 

20 


USES  OF  WAVE  METERS  21 

The  coupling  between  the  oscillatory  circuit  being  measured 
and  the  receptor  loop  of  the  wave  meter  should  not  be  any  greater 
than  necessary  to  get  a  readable  deflection  on  the  hot-wire 
instrument  or  galvanometer,  for  the  resonance  position.  Other- 
wise, the  instrument  or  the  thermo-j unction  may  be  injured. 
In  any  case,  no  matter  what  form  of  resonance-indicating  device 
may  be  used,  the  coupling  ought  to  be  as  loose  as  possible,  in 
order  to  avoid  any  back  influence  upon  the  exciting  circuit,  the 
frequency  of  which  would  be  affected  by  too  close  coupling. 

Measurement  with  Helium  Tube. — The  helium  tube  is  con- 
nected'to  the  terminals  of  the  condenser  of  the  wave  meter.  By 
changing  the  position  of  the  condenser  pointer  the  helium  tube 
is  brought  to  a  glow,  when,  by  approach  to  the  resonance  posi- 
tion, the  voltage  across  the  condenser  reaches  the  value  neces- 
sary to  make  the  tube  glow.  If  the  helium  tube  lights  up  dur- 
ing too  great  a  range  of  the  condenser  pointer,  it  is  a  sign  that 
the  wave  meter  is  coupled  too  closely  to  the  exciting  cricuit. 
The  receptor  loop,  or  flat  coil,  should  then  be  drawn  away  from 
the  exciting  circuit  until  the  helium  tube  glows  during  only  a 
very  short  movement  of  the  pointer  of  the  condenser. 

Measurement  with  Telephone  and  Detector,  or  Galvan- 
ometer and  Detector. — In  consequence  of  the  great  sensibility 
of  either  of  these  arrangements,  the  coupling  between  the  ex- 
citing circuit  and  the  wave  meter  must  be  very  loose.  The 
inductance  of  the  wave  meter  must  be  held  distinctly  farther 
away  from  the  exciting  circuit  with  this  arrangement  than  is 
possible  in  the  former  cases.  This  device  is  ordinarily  used  many 
yards  away  from  the  circuit  being  measured. 


CHAPTER  IV 
TUNING  THE  SENDING  STATION 

Disconnect  the  sending  condenser,  as  shown  in  Fig.  18,  and 
connect  the  lower  end  of  the  helix  through  the  spark  gap  to 
ground.  The  secondary  of  the  transformer  is  connected,  to  the 
spark  gap.  The  wave  meter,  W,  is  brought  near  the  helix,  and 
loosely  coupled  to  it.  The  antenna  is  connected  by  a  clip  contact 
to  some  particular  number  of  turns  of  the  helix,  and  the  sending 
key  is  depressed,  making  long  dashes  and  producing  a  spark  at  the 
gap.  This  sets  up  oscillations  in  the  antenna  circuit,  and  the 


Antenna 


Method  of  determining  Wave 
Length  of  antenna  circuit 


Helix 


I   [   I    |    I   |    I   |   I   |  Condenser  disconnected 


Transformer 

j  LMMMMJi 


FIG.  18. 

wave  meter  is  adjusted  to  resonance  with  the  exciting  circuit. 
The  wave  length  is  read,  and,  with  the  corresponding  number  of 
turns  of  helix,  is  entered  in  a  table.  The  spark  gap,  during 
these  measurements,  should  ordinarily  be  used  with  the  smallest 
sparking  distance  that  can  be  used  without  maintaining  an  arc 
rather  than  a  spark.  The  clip  contact  is  now  moved  to  another 
point  on  the  helix,  thus  putting  more  or  less  inductance  in  the 
circuit,  and  the  wave  length  is  again  determined  and  entered, 
with  the  number  of  turns  of  helix,  in  the  table.  It  is  well  to 
start  with  all  the  turns  of  helix  in  series  with  the  antenna,  spark 

22 


TUNING  THE  SENDING  STATION //-.  '     '-  '"'< 


gap  and  ground,  and  gradually  reduce  the  number,  one  turn  at 
a  time,  until  no  turns  remain,  and  there  is  nothing  in  the  circuit 
but  the  antenna,  spark  gap  and  ground.  In  measuring  the  aerial 
of  a  quenched  spark  station,  an  ordinary  Marconi  gap  should 
be  used  instead  of  the  quenched  gap. 

It  will  be  found  a  trifle  difficult  at  first  trial  to  measure  the 
wave  length  of  the  aerial  when  no  turns  of  helix  are  included, 
except  when  the  detector  and  telephone  are  used  as  a  detecting 
device.  The  wave  meter  will  have  to  be  brought  rather  close 
to  a  half-turn  of  the  wire  leading  to  aerial  or  ground,  if  the 
helium  tube  is  used,  since  it  is  not  nearly  as  sensitive  as  the 
hot-wire  ammeter,  or  the  telephone  and  detector,  as  a  receiving 
device.  When  these  are  used  the  coupling  with  the  half-turn 


Method  of  determining  Wave 
Length  of  exciting  circuit 


l^-orv—YY-J  */    I  Ground 

jnrTOyTTT]j  disconnected 

FIG.  19. 

in  the  aerial  wire  can  be  made  very  loose.  This  wave  length  of 
the  circuit,  containing  only  the  antenna,  spark  gap  and  ground, 
is  called  the  natural  wave  length  of  the  aerial.  The  natural 
period  of  the  aerial  is  the  time  necessary  for  one  complete 
oscillation  in  this  aerial  system,  without  any  turns  of  helix, 
and  is  measured  in  microseconds.  It  should  not,  as  is  fre- 
quently done  by  some  wireless  experts,  be  confounded  with  the 
natural  wave  length,  which  is  measured  in  meters. 

From  the  table  of  wave  lengths  just  formed,  the  results  are 
plotted  to  a  convenient  scale,  and  give  a  curve  like  that  marked,, 
"Antenna  Circuit/'  Fig.  20. 

The  condenser  circuit  is  then  measured  in  the  same  manner. 
In  this  case  the  antenna  and  ground  (see  Fig.  19)  are  disconnected; 


I 

;f$0":     WATTMETER  IN  WIRELESS  TELEGRAPHY 

and  the  condenser  circuit,  with  the  spark  gap  in  series;  is  connected 
with  various  numbers  of  turns  of  the  helix,  and  the  wave  length 
for  each  number  of  turns  is  determined,  and  a  curve  of  wave 
lengths  against  turns  is  plotted.  The  curve  for  this  case  is  put 
on  the  same  sheet  with  the  antenna  observations,  and  marked 
"Exciting  Circuit,"  Fig.  20. 


J 


3      4        5       6       7       8       9      10     11      12 
Turns  of  Helix 


0        1 

FIG.  20. — Tuning  curves  of  sending  station. 


By  a  reference  to  these  curves  we  can  now  obtain  the  number 
of  turns  required  either  in  the  condenser  circuit,  or  in  the  antenna 
circuit,  to  produce  a  given  wave  length. 

It  is  to  be  noted  that  the  tuning  curve  thus  found  for  the 
exciting  circuit,  is  correct  only  when  the  capacity  of  the  sending 
condenser  remains  the  same  as  when  the  measurements  of  the 


TUNING  THE  SENDING  STATION 


25 


exciting  circuit  were  made.  Hence  it  is  well  to  note  what  the 
capacity  is  at  this  time. 

To  illustrate  the  above  process  of  tuning  with  the  wave  meter, 
let  it  be  required,  at  the  station  for  which  the  curves  in  Fig.  20 
were  plotted,  to  tune  both  exciting  and  antenna  circuit  to  580 
meters. 

From  Fig.  20  it  is  seen  that  to  get  this  wave  length  in  the  ex- 
citing circuit,  one  must  use  8  turns  of  the  helix,  and  to  have  the 
same  wave  length  in  the  antenna  circuit,  when  alone,  one  must 
use  in  this  circuit  9|  turns.  Hence,  if  we  connect  the  condenser  and 


FIG.  21. 

spark  gap  leads  about  8  turns  of  helix,  and  the  antenna  and 
ground  leads  about  9J  turns  of  helix,  we  shall  have  the  two 
circuits  in  resonance,  and  powerful  oscillations  will  be  induced 
in  the  antenna,  but  there  may  be  two,  or  only  one  resultant 
wave,  sent  out  by  the  station,  depending  upon  how  closely,  or 
how  loosely,  the  two  circuits  are  coupled.  The  question  of 
coupling  will  be  referred  to  later. 

Another  method  of  measuring  the  wave  length  of  the  antenna 
alone  is  as  follows: 

The  antenna  is  excited  by  using  a  buzzer  in  circuit  with,  the 
coupling  turns  of  the  exciting  circuit,  and  the  wave  measured 


26 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


by  the  wave  meter,  using  the  telephone  as  the  indicating  device. 
Also,  the  wave  meter  may  be  used  as  an  oscillator,  and  induce 
oscillations  in  the  antenna  by  being  coupled  therewith.  An 
aperiodic  circuit  containing  the  detector  and  telephone,  and 
connected  inductively  to  the  antenna  (Fig.  21),  will  show  when 
resonance  is  obtained,  and  the  wave  length  determined  from  the 
position  of  the  wave  meter  pointer. 

Measurement  of  the  Wave  Lengths  of  the  Coupled  System.— 
As  stated  above,  the  open  and  closed  oscillatory  circuits  of  the 
sending  apparatus,  or,  as  they  have  heretofore  been  called  in 

this  paper,  the  "antenna"  and 
" exciting"  circuits,  if  coupled 
either  directly,  Fig.  22,  or  induc- 
tively, to  each  other,  emit  either 
one  or  two  waves  of  different 
lengths,  even  if  they  have  both 
been  previously  tuned  to  the 
same  wave  length. 

The  measurement  of  the  radi- 
ated wave  or  waves  of  a  coupled 
system  is  shown  in  Fig.  22. 
The  wave  meter  W  is  brought 
near  a  single  small  turn  in  the  an- 
tenna lead  of  the  station  and  the 
receptor  loop  placed  so  that  it 
is  parallel  to  this  loop,  and  at 

sufficient  distance  from  it,  so  that  the  wave  meter  circuit  will 
not  react  upon  the  sending  set.  For  a  correct  measurement  of 
the  radiated  waves  it  is  essential  that  the  wave  meter  be  operated 
only  by  the  currents  in  the  open  circuit.  The  correct  position 
for  the  wave  meter  with  reference  to  the  exciting,  or  closed 
circuit,  is  found  when,  upon  the  open  circuit  being  uncoupled 
from  the  closed  circuit,  the  wave  meter  is  found  to  be  unaffected 
by  the  closed  circuit.  Special  emphasis  is  laid  upon  this  correct 
method  by  the  Department  of  Commerce  in  its  instructions  to 
Radio  Inspectors,  who  are  concerned  only  with  the  radiated 
waves.  The  key  is  then  closed  for  a  long  dash  and  the  pointer 
of  the  wave  meter  moved  over  the  graduated  scale  until  resonance 
is  indicated  by  the  indicating  device  used.  This  will  generally 
be  the  longer  wave,  or  "  upper  hump,"  since  in  stations  so 
coupled  that  they  send  out  two  waves,  the  longer  wave  usually 


E       w      i 

£— pJUULq-J 

W 


FIG.  22. — Measurement  of  radiated 
wave  lengths  of  coupled  circuits. 


TUNING  THE  SENDING  STATION 


27 


contains  the  most  energy,  and  is  most  easily  found  with  the  wave 
meter.  To  locate  the  short  wave,  or  " lower  hump"  it  may  be 
necessary  to  bring  the  wave  meter  inductance  closer  to  the  an- 
tenna loop  than  before.  The  two  humps  of  closely  coupled  cir- 
cuits can  usually  be  shown  with  the  helium  tube,  but  as  this 
necessitates  close  coupling  of  the  wave  meter  with  the  exciting 
circuit,  errors  in  measurement  may  result.  The  telephone  and 
detector  is  a  far  more  accurate  indicator  for  locating  the  two 
humps,  since  very  loose  coupling  of  wave  meter  and  exciting 


300          400          500          600          700 
Wave  Lengths  in  Meters 

Close  coupling. 
FIG.  23. 


\  \ 

\n 

90 
80 
70 
60 
50 
40 
30 
20 
10 

0 

30 

1 

I  k 

1 

\ 

J 

r 

\ 

S 

/ 

^ 

* 

0    400    500    600    700 

Wave  Lengths  in  Meters 

Loose  coupling. 
FIG.  24. 


FIGS.  23  and  24. — Resonance  curves. 


circuit  can  be  used.  The  dynamometer  telephone  of  the  Pierce 
wave  meter  also  gives  good  results  in  this  respect. 

A  far  more  instructive  measurement  of  the  two  wave  lengths 
may  be  made  if  a  hot-wire  ammeter  or  wattmeter,  a  thermo-ele- 
ment  and  galvanometer,  or  a  detector  and  galvanometer,  are  at 
hand,  since  the  different  currents  in  the  wave  meter,  for  different 
settings  of  the  condenser  pointer  can  then  be  plotted  and  a  curve 
obtained  showing  whether  the  station  is  sending  out  one  or  two 
waves,  and  at  exactly  what  wave  lengths  the  two  resonance 
points  are  obtained.  Figs.  23  and  24  are  curves  obtained  by 
this  process. 

It  was  decided  that  the  station  above  mentioned,  would  be 


28  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

tuned  to  580  meters.  From  the  curves  (Fig.  20),  it  was  seen 
that  to  do  this  required  9J  turns  of  helix  in  the  antenna  circuit, 
and  eight  turns  in  the  exciting  circuit.  Then  these  turns  were  put 
in  circuit  as  stated,  and  the  circuits  were  coupled  as  closely  as  pos- 
sible; i.e.,  so  that  the  8  turns  of  the  exciting  circuit  were  common 
to  the  9J  turns  of  the  antenna  circuit.  The  wave  meter,  with 
hot-wire  ammeter  in  circuit,  as  in  Fig.  4,  or  with  a  shunted  hot- 
wire wattmeter  as  shown  in  Fig.  25,  instead  of  a  helium  tube, 
was  then  brought  near  a  single  small  turn  taken  in  the  antenna 
lead  (Fig.  22)  above  the  helix  of  the  station,  and  while  the  key 
was  depressed,  the  hot-wire  ammeter  was  watched  as  the  pointer 
of  the  condenser  was  turned  over  the  whole  scale,  in  order  to 
determine  roughly  where  the  position  of  resonance  which  would 
give -the  greatest  current  in  the  ammeter  might  be.  This  pre- 
caution is  taken  to  avoid  injuring  the  hot-wire  meter. 

The  wave  meter  should  not  be  so  near  the  loop  that  the 
pointer  of  the  hot-wire  meter  will  run  off  the  scale  when  resonance 
is  reached.  The  dash  made  by  the  sending  key  should  be  long,  and 
the  variable  condenser  moved  very  slowly,  as  all  hot-wire  instru- 
ments work  very  slowly,  and  an  error  in  the  measurement  of  the 
current  in  the  wave  meter  circuit  may  result  from  haste. 

Resonance  Curves. — Plotting  ammeter  or  wattmeter  readings 
as  ordinates  and  those  of  condenser  degrees  as  abscissae,  we  get 
what  is  called  a  resonance  curve  (Fig.  23).  If  wattmeter  read- 
ings are  used,  the  ordinates  plotted  would  be  values  of  72,  in- 
stead of  I  or  milliamperes,  as  shown  in  this  figure.  The  two 
humps  due  to  closely  coupling  the  antenna  and  exciting  circuits 
of  the  station  are  evident. 

Though  we  tuned  both  antenna  and  exciting  circuits  to  580 
meters,  we  find  that  the  station  is  now  sending  out  two  waves,  one 
longer,  and  one  shorter  than  580  meters.  One  measures  640 
meters  and  the  other  470  meters.  In  this  case  all  the  turns  of 
the  condenser  circuit  were  included  in  those  of  the  aerial  circuit, 
and  the  circuits  were  coupled  as  closely  as  possible.  Figure  24 
shows  a  resonance  curve  obtained  when  the  same  circuits  were 
loosely  coupled,  i.e.,  had  no  turns  in  common,  though  each 
circuit  had  the  same  wave  length  as  before.  Only  one  hump  is 
observed.  Its  maximum  ordinate  corresponds  to  practically  the 
same  wave  length  as  that  to  which  both  circuits  were  originally 
tuned,  viz.,  580  meters. 

A  word  of  caution  may  well  be  given  regarding  the  intensity 


TUNING  THE  SENDING  STATION  29 

of  the  humps.  They  are  not  to  be  taken  as  having  energy 
proportional  to  wave  meter  indications. 

If  a  series  of  resonance  curves  is  plotted,  the  coupling  between 
the  circuits  being  changed  slightly  for  each  succeeding  curve, 
the  evolution  of  the  single  hump  from  the  double  hump  can  easily 
be  traced. 

In  measuring  the  natural  wave  length  and  securing  tuning 
curves  of  a  station  employing  the  quenched  spark  system  of 
excitation,  the  quenched  spark  gap  must  be  replaced  by  an  ordi- 
nary spark  gap  for  the  purpose  of  measurement.  When  measur- 
ing the  closed  oscillatory  circuit  of  quenched  spark  transmitters 
having  variometers  in  circuit,  the  power  applied  to  the  primary 
during  the  measurements  should  be  reduced  as  much  as  pos- 
sible, to  avoid  puncturing  the  variometer  coils. 

Calculation  of  the  Percentage  of  Coupling  of  a  Coupled  System. 
—  As  stated  before,  when  two  circuits  are  tuned  to  a  common 
wave  length  A,  called  the  basic  wave  length,  and  coupled  together, 
unless  the  coupling  is  extremely  loose,  there  result  two  wave 
lengths,  <^i  and  ^2,  one  of  which  is  greater  than  the  basic  wave  A, 
and  the  other  less. 

While  loosening  up  the  coupling  has  the  distinct  advantage  of 
allowing  us  to  send  out  practically  a  single-valued  wave  length, 
nevertheless  we  are  obliged  to  take  into  consideratioa  the  slight 
loss  in  the  amount  of  energy  transferred  to  the  antenna  circuit, 
due  to  the  looseness  of  the  coupling.  In  practice  it  is  customary  to 
so  choose  the  coupling  that,  on  the  one  hand,  the  energy  received 
is  sufficiently  great;  on  the  other  hand,  that  the  two  resulting 
waves  are  not  too  far  apart. 

The  coupling  between  the  circuits  is,  ordinarily,  expressed 
as  a  per  cent.,  and  is  obtained  by  the  following  formula,  after 
we  have  found,  by  measurement  with  the  wave  meter,  the  values, 
/I,  to  which  both  circuits  were  tuned;  ^i,  the  longer  of  the  two 
resulting  waves,  and  ^2  the  shorter: 


Thus,  in  Fig.  23,  we  obtain  the  values  of  k,  ^,  and  ^2,  as  580, 
640  and  470,  respectively.  The  percentage  of  coupling  in  this 
case  is  — 

_  470 


58Q 


X  100  =  29.3  per  cent. 


30  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

The  percentage  of  coupling  found  by  the  above  method 
should  not  be  confounded  with  the  term  Coefficient  of  Coupling, 
sometimes  indicated  by  the  letter  T. 

The  value  of  T  is  found  from  the  equation — 


M2 


where  M  =  the  mutual  inductance  between  the  two  circuits, 

Lp  =  self-inductance  of  the  exciting  circuit,  and, 

Ls   =  self  -inductance  of  the  antenna  circuit. 

It  is  evident  that  these  quantities  are  difficult  to  measure 
accurately  in  the  case  of  the  sending  apparatus,  so  that,  instead 
of  finding  the  Coefficient  of  Coupling,  we  usually  find  the  per- 
centage of  coupling  of  the  sending  station  as  outlined  above. 

While  in  practice  it  is  usually  the  custom  to  measure  the  per- 
centage of  coupling,  it  is  practically  as  easy  to  determine  the 
Coefficient  of  Coupling,  if,  instead  of  using  the  equation  given 
above  for  finding  the  value  of  T,  we  measure  with  the  wave 
meter  the  basic  wave  length  ^,  and  the  resultant  wave  lengths, 
^,  and  ^2,  and  find  T  by  substituting  these  values  in  either  of 
the  derived  formulae: 


If  we  substitute  in  either  of  these  last  equations  the  values 
used  for  ^i  and  ^,  or  ^2  and  A,  in  tl^e  solution  of  the  equation 
previously  given  for  the  percentage  of  coupling,  it  will  be  seen 
that  the  values  of  T  and  K  are  not  identical,  or  the  coefficient 
of  coupling  is  not  the  same  as  the  percentage  of  coupling,  though 
the  average  value  of  T  found  by  solving  both  the  above  derived 
formulae  will  closely  approximate  that  found  by  the  practical 
method  of  finding  K  as  given  above. 


CHAPTER  V 

MEASUREMENT  OF  DAMPING  AND  LOGARITHMIC 
DECREMENT 

Since  the  passage  of  the  Act  to  Regulate  Radiocommunica- 
tion  in  the  United  States,  every  sending  station  is  required  to  be 
so  adjusted  that  the  logarithmic  decrement  per  whole  oscillation 
of  the  coupled  circuits  of  the  transmitter  shall  not  be  greater 
than  an  amount  fixed  by  law;  hence  it  is  important  that  a  prac- 
tical method  of  measuring  the  logarithmic  decrement  be  under- 
stood and  practised  by  all  persons  responsible  for  the  operation 
of  radio  stations  to  which  the  law  applies. 

A  definition  of  damping  and  logarithmic  decrement  has  been 

given  among  the  definitions  in 

the  earlier  part  of  this  book. 
(Cf.  page  2.) 

It  is  assumed  that  the  oscil- 
lations in  a  train  are  practi- 


cally  exhausted  when  the  last  K     il  Hot-wire 

.-.•,     ...                                   ji            -I  I            /Wattmeter 

oscillation  is  not  more  than  1  \  __  / 

per   cent,   of  the  initial  one.  FIG.  25. 

Fleming  has  shown  that  the 

number  of  complete  oscillations,  M,  in  a  train  is  given  by  the 

rule  — 


The  quantity  d  is  the  logarithm  of  the  ratio  of  two  successive 
oscillations  in  the  same  direction  to  one  another,  or,  2.303 
times  the  ordinary  logarithm  to  the  base  10  of  the  same  ratio. 
In  other  words,  it  is  the  logarithmic  decrement  per  whole  oscilla- 
tion, and  in  accordance  with  the  Act  passed  by  Congress,  this 
decrement  d,  shall  not  have  a  value  greater  than  0.2  "when 
measured  with  a  sensitive  wave  meter." 

The  very  simple  method  of  measuring  the  decrement  of  a 
transmitter  with  the  Marconi  Decremeter,  an  instrument 
designed  to  measure  this  quantity  directly,  will  not  be  given 

31 


32 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


Constantan 
Loop 


here,  as  full  directions  accompany  the  instrument  when  furnished 
by  the  manufacturer.  It  may  be  well  to  state  here,  for  the 
benefit  of  amateurs  and  other  experimenters,  that  an  instru- 
ment of  the  Decremeter  pattern  cannot  be  constructed  from 
data  given  in  magazines  with  any  hope  of  having  it  correctly 
calibrated  unless  it  be  compared  with  some  standard.  The 
wave  meter  method  here  given,  while  it  takes  a  little  longer,  will 
in  general  prove  more  satisfactory,  since  it  can  be  used  with 

practically  any  wave  meter, 
and  the  results  can  be  de- 
pended upon. 

In  order  that  a  wave  meter 
may  be  used  to  measure  the 
damping,  it  is  necessary  to 
provide  for  insertion  in  the 
wave  meter  circuit,  either  a 
thermoammeter  of  the  Duddell 
type  reading  from  about  0  to 
100  milliamperes,  and  having 
a  very  low  resistance,  prefer- 
ably not  more  than  one  ohm, 
or  a  thermo-element  of  simi- 
lar resistance  and  a  galvanom- 
eter (Fig.  5),  such  as  a  single 

pivot  Paul  galvanometer,  having  a  comparatively  low  resistance, 
or,  what  is  by  far  the  most  practical  method,  and  the  one  which 
has  the  advantage  of  giving  the  wave  meter  a  smaller  damping 
than  the  other  methods,  a  hot-wire  wattmeter  properly  shunted, 
or  inductively  coupled  to  the  wave  meter  circuit  (Fig.  25)  should 
be  used. 

The  thermo-element  necessary  for  use  with  the  galvanometer 
can  be  made  in  various  ways,  the  essential  point  in  the  construc- 
tion to  be  remembered  being  that  the  element  must  have  a  re- 
sistance of  not  over  one  ohm. 

A  simple  form  of  thermo-element  can  be  made  as  follows: 
Two  heavy  copper  wire  leads  are  brought  through  a  block  of 
hard  rubber  of  convenient  size  and  soldered  to  double  binding 
posts  on  the  block  for  the  purpose  of  making  connection  with  the 
wave  meter  circuit.     (See  Fig.  26.)     The  same  binding  posts 
serve  to  connect  the  thermo-element  to  the  galvanometer. 
The  copper  wires  project  from  the  base  as  shown  and  are 


FIG. 


26. — Iron-constantan  t  h  e  r  m  o- 
element. 


DAMPING  AND  LOGARITHMIC  DECREMENT  33 

brought  up  side  by  side  and  about  5  mm.  apart.  A  short  piece 
of  fine  iron  wire  in  the  form  of  a  V  or  loop  is  soldered,  as  shown 
in  the  drawing,  to  one  of  the  copper  wires,  and  a  similar  loop  of 
fine  constantan  wire,  about  0.02  mm.  in  diameter,  looped  through 
and  touching  the  iron  wire,  is  soldered  to  the  other  copper  wire. 
The  length  of  the  loops  of  iron  and  constantan  wires,  and  the 
degree  of  tension  with  which  one  loop  is  drawn  against  the  other' 
will  have  to  be  determined  by  experiment,  as  the  resistance  of 
the  element  is  measured  on  a  slide-wire  bridge,  or  other  form  of 
resistance  measuring  instrument.  The  resistance  of  the  completed 
element  should  not  be  greater  than  one  ohm. 

Any  other  form  of  thermo-element  may  be  used  for  damp- 
ing measurements  provided  the  resistance  is  not  above  one 
ohm. 

Such  elements  as  that  described  above,  on  account  of  the  nature 
of  their  construction,  cannot  be  calibrated  by  means  of  direct 
currents,  but  may  be  compared,  at  least  over  the  range  of  the 
larger  high  frequency  currents  with  a  sensitive  hot-wire  meter  in 
the  same  circuit  with  it,  e.g.,  in  a  wave  meter  circuit;  the  current 
received  by  the  wave  meter  when  coupled  to  an  oscillatory  send- 
ing circuit,  being  varied  by  changing  the  position  of  the  pointer 
of  the  wave  meter,  thus  producing  different  values  of  the  cur- 
rent in  the  wave  meter  and  thermo-element  galvanometer,  the 
current  directly  read  on  the  hot-wire  ammeter  being  the  current 
producing  the  corresponding  deflection  of  the  thermo-element 
galvanometer.  Squaring  the  values  of  the  currents  read  on  the 
hot-wire  meter  when  the  thermo-element  and  galvanometer 
are  in  circuit,  we  then  plot  a  curve,  the  abscissae  of  which  repre- 
sent the  scale  readings  of  the  galvanometer,  and  the  ordinates, 
the  square  of  the  values  of  the  current  in  the  circuit.  Hence,  if 
we  subsequently  pass  oscillations  through  the  thermo-element, 
the  reading  of  the  galvanometer  enables  us  to  determine  the 
value  (72)  of  these  oscillations  at  once. 

To  measure  the  damping  of  any  circuit  it  will  be  necessary 
to  open  the  circuit  of  the  ordinary  wave  meter  and  insert  in  it 
the  thermo-element  and  its  galvanometer.  Some  wave  meters 
still  in  use  are  not  primarily  intended  for  making  damping 
measurements,  so  no  binding  posts  may  be  found  available  for 
the  insertion  of  the  thermo-element,  and  other  means  will  have 
to  be  improvised.  In  the  Pierce  instrument,  the  element  may 
be  inserted  in  series  with  the  dynamometer  telephone,  or,  better 


34 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


still,  the  telephone  may  be  omitted  and  the  wave  meter  re- 
calibrated. 

Measurement  of  Damping  of  a  Closed  Oscillatory  Circuit. 
— The  wave  meter,  with  thermo-element  and  its  galvanometer  in 
circuit,  as  in  Fig.  5,  is  coupled  with  the  oscillatory  circuit  to  be 
measured,  and  a  resonance  curve  may  be  obtained  by  plotting 
the  readings  72  corresponding  to  the  various  galvanometer  de- 
flections observed  for  various  values  of  wave  length  obtained 
from  the  readings  of  the  wave  meter;  the  values  of  I2  being 
plotted  as  ordinates,  and  wave  lengths  as  abscissae.  Fig.  27 
shows  such  a  curve.  (If  a  wattmeter  be  used  instead  of  a 


l 

/ 

\ 

/ 

\ 

/ 

\ 

/ 

\ 

h 

3 

H 

y 

V 

' 

/i 

/ 

\ 

\ 

^ 

/ 

xf 

V 

\ 

i, 

r- 

X 

1 
1 

Vs 

^ 

r- 

s 

5 

1 

'  i 

/I 

1 

rtsh 

.i 

, 

2 

; 

4] 

0 

4X 

50 

41 

0    44 

0    4£ 

>0    « 

•0    4^ 

0    48 

!0    4£ 

10    5( 

W   5] 

LO    6! 

JO   5£ 

JO    54 

0 

5.r 

0 

Wave  Lengths  in  Meters 

FIG.  27. 

thermo-element  and  galvanometer  note  that  the  readings  of  the 
instrument  do  not  have  to  be  squared  as  the  readings  are  them- 
selves the  squares  of  the  current.) 

It  will  be  seen  that  the  readings  of  the  galvanometer  increase 
with  the  wave  lengths,  until  a  maximum  I2m  is  reached  corre- 
sponding to  a  wave  length,  Xm.  Then  after  passing  the  maximum 
value  of  the  current,  the  readings  fall  off  in  value  as  we  depart 
further  from  exact  resonance. 

Let  Pm  be  the  square  of  the  current  in  the  wave  meter  read 
from  the  calibration  curve  of  the  galvanometer  corresponding 
to  the  wave  length  Xmj  when  exact  resonance  is  obtained,  and 
let  72  be  the  square  of  the  current  in  the  circuit  corresponding 


DAMPING  AND  LOGARITHMIC  DECREMENT  35 

to  any  other  wave  length  ^i.  Now  the  oscillation  circuit  under 
test  has  a  certain  decrement  $1,  and  the  wave  meter  itself  has  a 
certain  decrement  £2. 

V.  Bjerknes  has  shown  that  the  following  relation  holds  good 
between  the  decrements  of  the  two  circuits,  and  the  wave  lengths 
Xm  and  ^i  (when  the  currents  I2m  and  72  were  obtained),  pro- 
vided that  Xm  and  Xi  do  not  differ  from  one  another  by  more  than 
say  5  per  cent.;  and  that  ^i  is  less  in  value  than  Am. 


^•^HS^CT 


This  formula  is  true  only  provided  $2  is  small  in  comparison 
with  &L 

If  it  be  desired  to  use  the  condenser  readings  of  the  wave 
meter,  instead  of  the  wave  lengths,  as  is  commonly  done  by 
radio  engineers  in  this  country,  the  formula  becomes, 


where  Cm  and  C\  are  the  capacities  of  the  wave  meter  condenser 
corresponding  to  km  and  Ax  in  the  first  equation.  Condenser 
scale  readings  in  degrees  may  also  be  used,  as  explained  later. 

In  plotting  the  resonance  curve  described  above,  it  is  usual 
to  take  I2m  as  unity  and  72  as  a  decimal  part  of  72m. 

The  formula  for  the  damping  given  above  becomes  greatly 
simplified  for  practical  purposes,  and  gives  accurate  enough 
results,  if,  instead  of  plotting  the  complete  resonance  curve,  we 
change  the  variable  condenser  so  that  for  a  wave  length  ^ithe 
galvanometer  deflection  will  have  fallen  to  \  what  it  was  at 
the  resonance  position,  i.e.,  so  that  72  =  |  72m.  (If  the  current 
is  read  with  a  hot-wire  instrument  of  not  more  than  one-ohm 
resistance  reading  directly  in  amperes,  then  the  reading  of  the 

meter  corresponding  to  >*i  should  be  of  that   correspond- 

ing to  >L,  since  1.414  =  \/2).  Then  in  the  above  equation 
the  quantity  under  the  radical  becomes  unity  and  the  formula 
takes  the  simplified  form: 


36  WAVE  METER  IN  WIRELESS  TELEGRAPHY       , 

Since  the  resonance  curve  is  not  quite  symmetrical  with  respect 
to  its  maximum  ordinate  it  is  best  to  determine  the  values  of  the 
wave  length  >^i,  lying  on  either  side  of  the  maximum  ordinate 
which  correspond  to  J/2TO,  and  to  take  the  mean  of  these  values 
to  be  put  into  the  above  formula.  Using  capacity  readings 
instead  of  wave  lengths  the  mean  value  is  given  by  the  formula 


where  C2  and  Ci  are  values  found  on  either  side  of  Cm,  when  the 
wattmeter,  ammeter,  or  galvanometer  readings  fall  from  P  to 

I2 

~n.     This  is  the  most  practical  method,  and  most  direct. 

The  measurement  gives  the  sum  of  the  dampings  of  the  wave 
meter  and  of  the  oscillatory  circuit  being  measured.  To  get  the 
damping  ^i,  of  the  latter  circuit  alone,  it  will  be  necessary  to 
subtract  the  wave  meter  damping,  d2)  from  the  result  obtained. 


EXAMPLE:  USING  WAVE  METER  WITH  GALVANOMETER 
AND  THERMO-ELEMENT  (FIG.  5) 

Galvanometer  deflections  are  proportional  to  72,  but  actual 
currents  are  not  to  be  measured. 

Formula  used  ^  +£2  =  2^(1  —  y^J  where  Am  is  greater  than  ^. 

\  // 


Let  D  =  initial  deflection  of  galvanometer  obtained  when  km 
is  reading  of  wave  meter  for  resonance. 

EXAMPLE 

Suppose  D  =  100  scale  divisions  when  /lm  =  500  meters.  Re- 
duce scale  reading  of  galvanometer  to  JD  =  50  scale  divisions 
in  this  case,  by  turning  condenser  handle  of  wave  meter. 

Read  from  wave  meter  scale  the  wave  length  >^i  =  488  m. 
corresponding  to  this  deflection  on  galvanometer. 

Substituting  values  in  the  formula  above,  the  joint  damping 


(l  - 


=  6.2832l  -    ~    =0.1508 


For  accuracy  the  pointer  should  also  be  brought  from  the 
resonance  position  to  a  wave  length  greater  than  Am  which  will 


DAMPING  AND  LOGARITHMIC  DECREMENT  37 

also  give  a  deflection  JD  and  the  values  of  hm  and  ^i  so  found 
substituted  in  the  formula  which  becomes  dl-}-d2  =  2n\l  -    r- 

for  this  case. 

The  two  values  of  ^1+^2  thus  found,  should  be  averaged  to 
get  the  mean  value  of  the  joint  damping. 

If  £2  =  damping  of  the  wave  meter,  is  known,  subtract  this 
value  from  that  just  obtained,  which  gives  value  of  the  damping 
of  the  circuit  measured.  Thus  if  dz  =  0.0192,  we  at  once  get  di  = 
0.1508-0.0192  =  0.1316  as  the  damping  of  the  circuit  being 
measured. 


DAMPING  MEASUREMENT  USING   THERMOAMMETER   (FIG.  4) 
INSTEAD  OF  GALVANOMETER 


Formula  ^+^2  =2w  l- 


Let  D  =  initial  reading  of  the  thermoammeter  corresponding 
^m. 

Suppose  D  =  100  milliamperes.     Xm  =  500  m. 
Reduce    scale    reading     on   thermoammeter    to    the    value 

=70.7  milliamperes  when  >*i  = 


1.414     1.414 

Then  #i+£2  =  6.2832   l-          =0.1508. 


The  other  value  of  <^i+<^2  would  be  found  as  with  thermo- 
element and  galvanometer,  and  the  mean  value  of  the  damping 
determined.  As  before,  knowing  the  value  £2,  subtract  it  from 
the  value  just  obtained  to  get  the  logarithmic  decrement  of  the 
circuit  measured. 

DAMPING  MEASUREMENT  USING  HOT-WIRE  WATTMETER 

The  wattmeter  is  connected  to  the  wave  meter  as  shown  in 
Figs.  17  and  25.  Condenser  capacities,  instead  of  wave  lengths, 
are  read  from  a  curve  or  table  of  capacities  made  for  the  wave 
meter  condenser  showing  the  capacity  corresponding  to  any 
degree  reading  of  the  scale.  It  is  immaterial  whether  the  ca- 
pacity be  recorded  in  centimeters  or  in  microfarads.  The  watt- 


38 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


meter  readings  are  in  watts,  equal  to  PR,  and  are  purely  'rela- 
tive. Since  special  alloy  wire  is  used  in  the  construction  of  the 
wattmeter,  R  does  not  change  by  heat  within  the  range  of  the 
scale  on  the  meter,  hence  the  instrument  may  be  considered  as 
showing  directly  the  values  of  P. 
Formula 


Suppose  the  wattmeter  reads  0.030  when  Cm  =  0.00120  mfd. 
at  resonance,  and  that  Ci  =  0.00118  mfd.  and  C2  =  0.00123  mfd. 
are  the  two  values  obtained  after  moving  the  condenser  pointer 
to  left  and  right  of  the  resonance  position,  respectively,  until 


Degrees 
FlG.   28. 

the  wattmeter  in  each  case  reads  one-half  what  it  did  at  the 
resonance  position,  or  0.015. 

Substituting  in  the  formula  we  get 


and  knowing  £2  we  at  once  get  the  logarithmic  decrement  of  the 
circuit  measured. 

Radio  engineers,  in  actual  practice,  use  the  condenser  read- 
ings in  degrees  directly,  provided  the  condenser  of  the  wave 
meter  has  a  straight  line  calibration.  A  condenser  with  plane 


DAMPING  AND  LOGARITHMIC  DECREMENT  39 

semi-circular  plates  will  have  a  straight  line  for  its  calibration 
between  approximately  10°  and  170°  as  shown  in  Fig.  28,  and, 
if  the  straight  line  be  extended  back  of  the  capacity  axis  as 
shown,  it  will  cut  the  other  axis,  or  scale  of  degrees,  at  a  point 
about  3°,  4°,  or  5°,  to  the  left  of  the  origin,  or  zero;  hence  within 
the  limits  10°  and  170°,  capacities  will  vary  as  the  condenser 
readings  in  degrees,  plus  3°,  4°,  or  5°,  as  the  case  may  be,  depend- 
ing upon  the  particular  condenser  used.  This  is  the  usual 
method,  the  value  to  be  added,  as  +4°,  generally  being  given 
with  the  calibration  by  the  maker,  as  in  the  case  of  the  E.  G.  W. 
meter  of  the  Telefunken  Co.,  where  the  value  to  be  added  is 
given  as  +4°. 

Suppose  we  were  to  measure  the  logarithmic  decrement  by 
using  condenser  degrees,  and  that  the  condenser  used  had  a 
calibration  curve,  which,  if  prolonged  would  strike,  as  in  Fig.  28, 
a  point  4°  to  the  left  of  the  C  axis. 
Formula 


l2~2  C°m+4° 

Suppose  C°m  =  150.0°,  C°i  =  146.2°,  and  C°2  =  154.8°,  and  that 
these  values  are  found,  by  reference  to  our  calibration  curve  of 
capacities,    to    correspond    to    0.00250,    0.00244,    and    0.00258 
microfarads,  respectively. 
Substituting 

r  °-088- 


If,  instead  of  using  condenser  readings  in  the  formula,  we  had 
used  capacities  the  result  would  have  been  practically  the  same; 
for,  substituting  the  capacity  values  we  get 

*  ft-Ci     n  0.00258-0.00244 


0.00250 


The  method  using  condenser  degrees  is  as  accurate  as  that 
using  capacities,  and  recommends  itself  as  being  the  quickest  of 
all  methods  for  measuring  the  decrement. 

1  The  value  of  the  self-damping,  dZj  of  the  wave  meter  is  not 
furnished  by  all  makers  of  wave  meters.  For  the  E.  G.  W.  meter 
of  the  Telefunken  Co.,  the  damping  of  the  wave  meter  for  the 
various  spools  is  about  as  follows: 


40  WAVE  METER  IN  WIRELESS  TELEGRAPHY 


Spool  I 

0.046 

Spool  II 

0.040 

Spool  III 

0.024 

Spool  IV 

0.023 

Spool  V 

0.017 

Spool  VI 

0.019 

where  spool  I  is  for  the  shortest  wave  lengths  and  spool  VI 
for  the  longest. 

For  exact  measurement  with  any  wave  meter  the  self-damping 
of  the  wave  meter  must  be  determined  by  the  method  given  below. 
It  is  absolutely  necessary  in  the  measurement  of  the  damping  to 
work  with  a  constant  coupling,  and  to  take  care  that  the  energy  in  the 
primary  circuit  is  as  constant  as  possible.  If  the  coupling  between 
the  exciting  circuit  and  the  wave  meter  is  too  close,  the  damping 
will  have  too  great  a  value.  If  there  is  any  doubt  as  to  whether 
the  coupling  was  loose  enough,  measurements  are  made  using 
two  different  couplings.  If  the  smaller  value  is  obtained  with 
the  looser  coupling,  then  it  is  evident  that  the  coupling  was  too 
close  during  the  first  measurement. 

Determination  of  the  Self-damping  of  the  Wave  Meter. — 
The  sum  of  the  dampings  of  both  circuits  (^1+^2)  having  been 

found  as  stated  above,  a  fine  wire  non- 
inductive  resistance,  R,  Fig.  29,  is  in- 
serted in  the  wave  meter  circuit  and  an- 
other measurement  of  the  sum  of  the 
dampings  of  the  exciting  circuit  and  the 
wave  meter  is  made,  the  position  of  the 
wave  meter  with  reference  to  the  ex- 
citing circuit  being  exactly  the  same 
as  in  the  former  measurement.  After 
the  insertion  of  the  resistance  the 
reading  of  the  thermo-element  galvanometer  or  of  the  wattmeter 
falls  from  I2m  to  the  value  I2m2  at  the  resonance  position  pre- 
viously found.  In  order  to  make  the  measurements  sufficiently 
accurate  it  is  necessary  to  put  in  so  much  resistance  that  Izmz 
will  become  about  \  I2m  (Fig.  27). 

The  damping  of  the  wave  meter  has  been  increased  by  an 
amount  £'2,  and  the  sum  of  the  dampings  now  measured  equals 
(^1+^2+^2),  instead  of  (^i+£2)  as  before.  The  same  method 
of  procedure  is  followed  for  finding  the  sum  (^1+^2+^2)  as  was 


DAMPING  AND  LOGARITHMIC  DECREMENT  41 

used  in  finding  (^1+^2),  i-e.,  from  the  resonance  position  corre- 
sponding to  72m2  the  current  is  reduced  to  J  /2m2  by  turning 
the  handle  of  the  wave  meter,  and  the  wave  length  or  the  ca- 
pacity for  the  resonance  position  and  that  corresponding  to  the 
wave  length  A2  or  the  capacity  C3  is  read  from  the  scale  when  the 
current  in  the  wave  meter  /22  is  equal  to  i  72m2  and  the  values 
are  inserted  in  the  formula, 

=2*(1-£D- 


where  X2  and  Xm  are  the  wave  lengths,  or  C3  and  Cm  the  capaci- 
ties found  after  insertion  of  resistance,  R,  in  wave  meter,  Xm 
and  Cm  being  the  same  as  before.  Knowing  the  values  of  (^1+^2) 
and  of  (^1+^2+^2),  it  is  a  simple  matter  to  get  £'2,  which  is  equal 
to  the  difference  between  these  two  sums. 

In  using  capacities  instead  of  wave  lengths  it  is  much  more 
convenient  to  use  the  combined  formula 


where  C3  and  C4  are  the  capacity  values  found  on  either  side  of 
Cm,  after  the  introduction  of  the  resistance  wire  into  the  wave 
meter  circuit,  when  the  current  is  reduced  from  72m2  to  %  Pm^ 

If  we  put  X  for  (<?i+£2)  and  X'  for  (^+^2+^2),  the  value 
of  ^2  can  be  obtained  from  the  following  formula: 


and  since  X  =  di 


Hence,  substituting  in  this  equation  the  value  of  #2  found  as 
above  we  arrive  at  the  decrement  of  the  circuit  under  test. 

EXAMPLE:  TO  FIND  DAMPING  OF  THE  WAVE  METER 

Using  Thermo  -element  and  Galvanometer.  —  Piece  of  resist- 
ance wire  (about  ten  inches  of  No.  26  Climax),  with  sliding  con- 
tact for  varying  length  of  wire  used,  is  introduced  into  wave 
meter  circuit.  When  this  resistance  wire  is  inserted  in  the  wave 
meter  circuit  there  must  be  no,  or  only  a  very  short,  free  end  to 


42  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

this  wire,  as  otherwise,  if  the  sliding  contact  picks  off  only  a 
small  part  of  this  wire  a  very  serious  error  may  sometimes  be 
made.  The  wire  can  be  shortened  accordingly. 

Wave  meter  pointer  again  set  to  value  of  Xm  found  in  for- 
mer example  (500  m.),  and  left  there. 

While  key  is  depressed,  adjust  sliding  contact  on  resistance 
wire  until  galvanometer  deflection  is  reduced  to  \  D  =  50,  in 
this  case. 

Having  thus  determined  right  amount  of  resistance  wire,  turn 
condenser  pointer  of  wave  meter  until  galvanometer  shows 
deflection  J  D  =  25  in  this  case. 

Read  corresponding  wave  length  ^2  =  486  meters. 

Then  di+dt+d'i  =  27r(l-^)  =  6.2832(l-~)  =.1664 

Let  ^1+^2+^2  =  X'  =  .  1664 
Average  value  ^1+^2  =  X  =.1508 


Then  the  difference  £'2  =  0.0156  =  damping  due  to  insertion  of 
resistance  wire.     Damping  of  wave  meter 

0.1664X0.0156 

~ 


~2Z-X'~(2X0.1508)-0.1664 

If  this  value  of  the  damping  has  been  carefully  determined  for 
the  particular  inductance  of  the  wave  meter  used,  it  can  be  marked 
on  the  instrument  for  future  reference,  and,  to  simplify  later 
damping  measurements,  the  damping  for  each  of  the  induc- 
tances of  the  wave  meter  should  be  determined  in  this  manner. 

To  Find  Damping  of  Wave  Meter  Using  Thermoammeter.  — 
Suppose  Xm  =  500  m.  Set  pointer  at  that  reading.  Resistance 
wire  introduced  into  wave  meter  circuit,  and  adjusted  so  that 

current  shown  on  ammeter  falls  to  value   ..  41  4  ~  70-7  milli- 

amperes. 
Leaving  resistance  unchanged,  move  wave  meter  pointer  un- 

til current  -~  =  50  milliamperes  is  shown  on  ammeter.     Then 

^2  is  found  to  be  equal  to  486  meters. 

Proceed  as  with  thermo-element  and  galvanometer  to  find 
damping  of  wave  meter  by  substitution  of  these  values  in 
formulae. 


DAMPING  AND  LOGARITHMIC  DECREMENT  43 

To  Find  Damping  of  the  Wave  Meter  Using  the  Wattmeter.— 
Let  C°m,  as  in  the  example  before  given,  where  the  wattmeter 
was  used  to  measure  the  damping,  equal  the  scale  reading  of 
the  condenser,  in  degrees,  at  the  resonance  position.  This  was 
found  to  be  150.0°.  Set  condenser  pointer  at  that  reading. 
Resistance  wire  is  introduced  into  the  wave  meter  circuit  as  de- 
scribed for  thermo-element  and  galvanometer,  and  adjusted  so 
that  the  energy  shown  on  the  wattmeter  falls  to  one-half  the 
former  reading  at  resonance;  in  this  case  0.015  watts. 

Leaving  the  resistance  unchanged,  move  the  condenser  pointer 
first  to  the  right  and  then  to  the  left  of  the  resonance  position, 
and  note  the  readings  of  the  condenser,  C°4  and  C°3,  respectively, 
when  the  wattmeter  reading  in  each  case  has  fallen  to  one-half 
the  reading  for  resonance  with  the  resistance  in  circuit;  in  this 
case  0  .  0075  watts. 

Suppose  C°4  =  155.6°  and  C°3  =  145.35° 

Substituting  in  formula 

6  °=0.1045 


Proceeding  as  before  described  for  thermo-element  and  galva- 
nometer, by  substituting  in  the  formulae  given  the  values  already 
found,  we  determine  the  damping  of  the  wave  meter,  £2,  to  be 
0  .  024  for  the  coil  used  in  this  case. 

If,  instead  of  using  condenser  degrees,  we  use  actual  capacities, 
the  formula  used  would  be 


[>/  \ 

'2)  =2 


and  §2  would  be  found  as  described  above. 

While  the  method  of  using  capacities  instead  of  wave  lengths 
has  been  given  only  in  illustration  of  the  method  of  making 
measurements  of  the  decrement  with  a  wave  meter  using  a 
wattmeter  for  measuring  the  relative  energy,  it  is  evident  that 
this  simple  capacity  measurement  can  be  just  as  easily  used  when 
a  thermo-ammeter  or  a  galvanometer  and  thermo-element  are  em- 
ployed, not  only  for  measuring  the  damping  of  any  radiating  cir- 
cuit but  of  the  wave  meter  itself,  and  it  is  recommended  to  the 
reader  as  the  most  practical  method  in  every  day  use,  and  the 
shortest  method  with  the  exception  of  the  direct  measurement 
with  a  decremeter. 


44  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

Determination  of  the  Resistance  of  the  Spark  Gap. — If,  in 
any  case  just  cited,  the  inductance  of  the  oscillatory  circuit  in 
centimeters  is  known,  or  can  be  measured,  and  the  high  frequency 
resistance,  R,  of  the  inductance  can  be  calculated  from  the 
dimensions  of  the  wire,  it  is  possible,  knowing  the  value  of  dly 
and  the  frequency  N  corresponding  to  resonance,  to  calculate 
the  resistance  of  the  spark  gap  from  the  following  formula: 

_2NLd1     __ 
10* 

where  R  and  r  are  measured  in  ohms. 

Determination  of  the  Approximate  Number  of  Complete  Oscilla- 
tions in  a  Wave  Train  before  the  Amplitude  of  the  Oscillations 
Falls  to  o.oi  of  the  Maximum. — Having  found  that  the  value  of  #1 
for  the  circuit  in  one  case  cited  was  0.1316,  from  the  formula 

4.605+di_4.6Q5+0.1316_ 
*i  0.1316 

it  is  seen  that  each  train  comprised  about  35  complete  oscillations. 

Measurement  of  the  Damping  of  a  Coupled  System. — This  is 
the  ordinary  case  where  it  is  necessary  to  determine  the  damping 
of  a  coupled  system  consisting  of  an  antenna  circuit  and  an  excit- 
ing circuit  which  are  tuned  to  the  same  period.  If  the  system 
employs  the  ordinary  gap,  instead  of  the  quenched  spark  gap,  in 
the  exciting  circuit,  and  the  coupling  between  the  circuits  is 
not  very  loose,  there  result  two  wave  lengths,  as  before  shown, 
one  longer  and  the  other  shorter  than  the  wave  length  to  which 
each  of  the  circuits  was  originally  tuned.  If  these  two  wave 
lengths  lie  sufficiently  far  apart,  the  damping  of  each  hump  is 
measured  separately  by  the  method  described  for  the  measure- 
ment of  the  damping  of  a  closed  oscillatory  circuit  with  spark  gap, 
except  that  the  wave  meter  is  coupled  to  the  loop  in  the  antenna 
lead  above  or  below  the  antenna  helix,  and  in  a  position  not 
affected  by  the  primary  circuit,  as  in  measuring  the  radiated 
waves  (Fig.  22).  This  precaution  is  particularly  insisted  upon 
by  the  Department  of  Commerce  so  as  to  avoid  the  possibility 
of  a  false  measurement  of  the  decrement  due  to  the  proximity  of 
the  exciting  circuit. 

No  difficulty  will  be  encountered  in  measuring  coupled  cir- 
cuits where  the  coupling  is  extremely  loose,  or  a  quenched  spark 


DAMPING  AND  LOGARITHMIC  DECREMENT  45 

is  used  in  the  exciting  circuit,  since  there  will  be  practically  only 
one  hump. 

To  Reduce  the  Logarithmic  Decrement  of  a  Coupled  System 
found  to  be  Greater  than  the  Legal  Limit. — Having  measured  the 
damping  of  the  radiating  circuits  as  coupled,  and  found  it  greater 
than  0.2  per  complete  oscillation,  it  is  necessary  to  add  induct- 
ance in  order  to  decrease  it  or  to  loosen  the  coupling  in  order  that 
the  total  resistance  may  be  decreased.  If  it  is  not  practicable  to 
change  the  wave  length,  the  aerial  must  be  shortened  to  decrease 
its  capacity  while  retaining  the  same  wave  length  by  adding 
inductance.  Putting  a  condenser  in  series  with  the  aerial  pro- 
duces the  same  effect,  but  is  not  considered  the  best  practice, 
though  it  may  well  be  used  in  low  potential  oscillating  sets  that 
require  very  close  coupling.  Such  a  condenser  is  sometimes  used 
with  good  effect  in  certain  wireless  telephone  transmitting 
sets. 

Method  of  Procedure  in  the  Adjustment  of  the  Sending 
Station  to  Comply  with  the  Act  to  Regulate  Radiocommunica- 
tion  Approved  August  13,  1912. — 1.  Tuning  curves  are  made  as 
described  on  pages  22  and  23. 

2.  If  the  station  is  restricted  by  law  or  order  to  the  use  of  one 
definite  sending  wave  length,  say  600  meters,  the  number  of 
turns  necessary  in  antenna  and  exciting  circuits  to  secure  this 
wave  length  is  taken  from  the  tuning  curves  as  described  on  page 
25. 

3.  Plot  a  resonance  curve  using  fairly  loose  coupling  of  circuits 
and  note  whether  the  energy  in  the  smaller  hump,  if  there  are 
two  humps,  exceeds  10  per  cent,  of  that  in  the  larger;  i.e.,  if  the 
value  of  I2  calculated  from  the  reading  of  the  ammeter  or  read 
directly  from  the  wattmeter  in  the  wave  meter  circuit  when  in 
resonance  with  the  peak  of  the  smaller  hump  exceeds  10  per  cent, 
of  the  maximum  ordinate  I2  of  the  greater  hump.     If  it  does, 
the  station  is  not  using  a  "pure  wave"  as  defined  by  the  act  to 
regulate  radiocommunication,  and  the  coupling  must  be  loosened 
until  this  condition  is  fulfilled. 

In  making  this  measurement  and  that  in  paragraph  4,  the 
wave  meter  should  be  coupled  with  a  single  loop  above  or  below 
the  antenna  helix  and  in  a  position  not  affected  by  the  primary 
circuit,  but  only  by  the  radiating  circuit  (Fig.  22). 

That  this  is  the  correct  interpretation  of  the  definition  of  "pure 
wave,"  and  the  correct  method  of  determining  when  the  station 


46  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

is  emitting  a  "pure  wave,"  is  the  decision  given  to  the  author  by 
the  Department  of  Commerce  and  Labor,  with  the  assent  of  the 
Director  of  the  Bureau  of  Standards. 

4.  Having  found  from  the  resonance  curve  that  the  station  is 
using  a  "pure  wave,"  measure  the  damping  of  the  radiating  cir- 
cuits and  see  if  the  decrement  is  greater  than  0.2  per  whole  oscil- 
lation, the  limit  placed  by  law  on  all  stations. 

5.  If  the  decrement  is  too  great,  reduce  the  coupling  and  meas- 
ure again.     Reducing  the  coupling  will  usually  be  found  to  be 
the  only  correction  necessary,  but  if  this  should  fail  to  produce 
desired  results,  make  the  changes  outlined  in  the  first  paragraph 
on  page  45. 

6.  Adjust  the  spark  gap  until  the  hot-wire  meter  in  the  an- 
tenna circuit  shows  the  greatest  radiation,  all  other  adjustments 
remaining  fixed. 

7.  The  station  is  now  adjusted  in  compliance  with  regulations, 
and  orders  are  issued  to  permit  no  change  in  the  adjustments, 
unless  directed  by  higher  authority,  or  required  or  permitted 
by  regulations  or  by  law. 

Where  the  Wave  Length  is  not  Restricted  by  Law  or  Official 
Order. — Where  the  station  is  not  restricted  to  a  particular  wave 
length,  effort  should  be  made  to  find  the  adjustments  giving  the 
greatest  efficiency  regardless  of  resulting  wave  length. 

There  is  one  best  wave  length  for  every  station,  and  when  that 
is  determined,  the  greatest  radiation  is  usually  obtained. 

The  process  of  tuning  the  station  for  maximum  efficiency, 
utilizing  the  best  wave  length  for  the  station  is  as  follows: 

1.  Make  tuning  curves  of  antenna  and  exciting  circuits. 

2.  To  determine  which  of  the  wave  lengths  lying  within  the 
limits  of  the  curve  marked  "Antenna  Circuit"  will  give  the  best 
radiation,  it  will  be  necessary  to  have  a  hot-wire  meter  in  the 
antenna  circuit  for  noting  the  radiation,     (a)  If  the  oscillatory 
circuits  are  direct-coupled,  start  by  placing  the  lead  from  the 
spark  gap  on  some  turn  near  the  middle  of  the  helix,  and  to  the 
same  point  attach  the  ground  lead.     Leaving  these  two  leads 
fixed,  move  the  other  two,  one  to  one  side  and  the  other  to  oppo- 
site side  of  the  fixed  leads,  placing  successively,  one,  two,  three, 
etc.,  turns  in  the  aerial  circuit,  and  the  corresponding  number  of 
turns  in  the  exciting  circuit  required  for  resonance,  as  determined 
from  the  tuning  curves,  pressing  the  sending  key  and  noting  the 
reading  of  the  hot-wire  meter  in  the  antenna,  for  each  combina- 


DAMPING  AND  LOGARITHMIC  DECREMENT  47 

tion,  and,  by  comparison,  determining  which  wave  length  gives 
the  greatest  radiation. 

It  is  to  be  noted  that  the  coupling  is  always  kept  loose, 
and  approximately  the  same  throughout  all  these  measurements. 
The  combination  giving  greatest  radiation  under  these  conditions 
should  be  adopted  as  the  best  for  the  station,  so  far  as  wave 
length  is  concerned. 

(b)  If  the  oscillatory  circuits  are  inductively  coupled,  start 
by  placing  one  turn,  two,  three,  etc.,  in  succession  in  the  aerial 
circuit,  and  the  corresponding  number  of  turns  necessary  for 
resonance,  as  determined  from  the  tuning  curves,  in  the  exciting 
circuit;  being  careful  to  maintain  a  loose  and  constant  coupling 
throughout,  between  the  two  inductances.  As  before,  the  great- 
est radiation  shows  the  best  wave  length  to  use. 

3.  Having  determined  the  best  wave  length  in  this  manner, 
proceed  with  the  adjustment  of  the  station  as  outlined  in  para- 
graphs 3  to  7  of  the  preceding  case,  using  this  best  wave  length 
instead  of  the  600  meter  wave  length  there  mentioned. 


CHAPTER  VI 

MEASUREMENT  OF  WAVE  LENGTH  OF  THE 
RECEIVING  STATION 

The  Wave  Meter  as  a  Sending  Set. — The  calibration  of  a 
receiving  set  is  equally  as  important  as  the  calibration  of  the 
transmitting  apparatus,  for  the  operator  of  a  wireless  station 
should  know  what  different  adjustments  of  his  apparatus  he 
must  make  to  put  his  receiving  set  in  resonance  with  any  particu- 
lar wave  length  in  order  to  facilitate  rapid  " picking  up"  of 
widely  differing  wave  lengths  when  desirable  to  do  so. 

The  different  adjustments  of  the  various  apparatus  of  his 
receiving  set  corresponding  to  any  particular  wave  length  he 
takes  either  from  tuning  curves,  or  from  tables  of  adjustments 
prepared  for  the  particular  receiving  set  and  antenna  he  is  using, 
or,  not  being  provided  with  these,  and  having  a  wave  meter  at 
hand,  he  starts  the  buzzer  of  the  wave  meter  to  work  continu- 
ously, sets  the  wave  meter  pointer  for  the  desired  wave  length, 
and  bringing  the  receptor  loop  of  the  wave  meter  near  the  single 
turn  taken  in  either  antenna  or  ground  lead  (see  Fig.  30),  varies 
the  adjustments  of  his  receiving  apparatus  while  he  listens  in 
with  the  usual  telephone  receivers  of  his  receiving  set,  until  he 
hears  the  maximum  sound,  when  the  adjustments  of  the  various 
apparatus  of  the  receiving  set  can  be  noted  in  a  table  opposite  the 
wave  length  as  indicated  on  the  wave  meter.  Care  must  be 
taken  not  to  have  the  buzzer  so  close  as  to  act  directly  upon  any 
part  of  the  receiving  set. 

A  wave  meter  used  systematically  upon  a  receiving  set  will 
afford  an  operator  in  the  shortest  time,  a  better  knowledge  of 
tuning  than  can  be  obtained  in  any  other  way.  An  operator 
who  knows  exactly  what  adjustments  to  make  for  a  given  wave 
length  will  at  once  pick  up  a  station,  which,  he  is  told,  will  send 
with  that  wave  length,  whereas,  the  operator  without  knowledge 
of  this  sort,  or  data  from  which  to  secure  it,  may  spend  hours 
adjusting  his  receiving  apparatus  to  every  possible  adjustment 
but  the  right  one  for  the  strange  station  he  wants  to  hear. 

The  Telefunken  buzzers  as  before  stated  have  a  key  with  which 

48 


WAVE  LENGTH  OF  THE  RECEIVING  STATION 


49 


Morse  signals  may  be  sent  out  from  the  wave  meter.  This 
appears  to  be  about  the  quickest  way  to  teach  a  new  operator 
to 'operate  a  receiving  set,  for,  an  instructor  can  have  the  opera- 
tor " listening  in"  on  the  receiving  apparatus,  and,  placing  the 
wave  meter  far  enough  away  from  the  operator  so  that  the  buzzer 
note  will  be  inaudible  as  a  sound  wave  through  the  air,  and  coup- 
ling the  wave  meter  inductance  with  a  loop  in  the  antenna  lead, 
can  send  out  Morse  signals,  using  a  wide  range  of  wave  lengths  one 
after  another,  and,  in  each  case,  have  the  listening  operator  tune 
the  receiving  set  for  the  proper  reception  of  the  signals.  The 
action  of  the  different  elements  of  the  receiving  set  will  thus  be- 
come apparent,  and  this  practical  work  will  be  worth  a  great  deal 
more  than  any  amount  of  theoretical  instruction  that  the  opera- 
tor can  receive. 


w 


IF 

=Lr  T 


4 


FIG.  30. 

Calibration  of  a  Receiving  Set  Having  a  Double-slide  Tuning 
Coil. — The  two  bars  (Fig.  30)  on  which  the  sliding  contacts, 
A  and  B,  move,  should  be  divided  into  some  convenient  scale,  say 
tenths  of  inches,  which  should  be  permanently  marked  thereon. 
Couple  the  coil  of  wave  meter,  W,  with  single  loop,  L,  of  antenna 
lead,  and  having  started  buzzer  of  wave  meter  going  continuously, 
set  pointer  of  wave  meter  at  350  meters,  and  listening  in  on  tele- 
phone receivers,  T,  having  adjusted  detector,  D,  for  sensitiveness, 
move  sliders  A  and  B  away  from  G  (the  grounded  end  of  tuning 
coil)  until  sound  in  telephone,  T,  is  loudest.  See  if  any  re-ad- 
justment of  B  will  give  any  better  signal.  Having  maximum 
sound  in  telephone  receivers,  make  a  table  of  adjustments  like 
the  following: 


50  WAVE  METER  IN  WIRELESS  TELEGRAPHY 


Wave  length  meters 

Antenna  slider  A 

Detector  slider  B 

350 
400 

5 

8 

20 

22 

and  so  on;  setting  the  wave  meter  for  every  25  or  50  meters  of 
the  scale,  in  turn,  and  writing  in  above  table  the  corresponding 
adjustments  for  every  25  or  50  meters  until  the  A  slider  reaches 
the  end  of  the  coil  farthest  from  the  grounded  end  G.  It  will  be 
noted  that  there  are  many  combinations  of  receiving  adjustments 
which  will  give  the  same  wave  length.  The  proper  one  to  use  in 
actual  work  for  best  results  will  only  be  found  by  actual  practice 
with  the  set.  It  will  also  be  seen  that  the  receiving  set  will 
always  be  in  resonance  with  two  or  more  waves  at  once,  and  it 
will  easily  be  seen  that  such  a  tuning  coil  will  always  be  liable 
to  the  greatest  amount  of  interference,  in  other  words,  is  not  very 
selective. 

Calibration  of  Inductive  Type  Receiving  Set  Having  an 
Untuned  Secondary  and  Variable  Primary. — These  inductive 
tuners  are  usually  made  so  that  the  coupling  between  the  primary 
and  secondary  coils  can  be  varied,  either  by  withdrawing  the 
secondary  from  the  primary,  or,  by  rotating  the  secondary  so 
that  its  turns  may  be  moved  through  any  angle  from  0  to  90° 
with  reference  to  the  turns  of  the  primary.  The  closest  coupling, 
in  the  latter  system,  being  obtained  when  the  coils  of  the  second- 
ary are  parallel  to  those  of  the  primary.  The  number  of  turns 
in  the  primary  may  be  varied  either  by  a  sliding  contact  moving 
on  a  rod  parallel  to  the  axis  of  the  primary  tube  and  touching 
the  different  turns,  or,  a  switch  arm,  or  pair  of  switch  arms, 
moves  over  a  series  of  switch  points  by  means  of  which  any  de- 
sired number  of  turns  of  wire  may  be  cut  into  the  primary  circuit. 
In  the  first  case,  where  the  bar  with  sliding  contact  is  used,  this 
bar  should  be  graduated  into  tenths  of  inches,  so  that  the  exact 
position  of  the  sliding  contact  can  be  determined  by  reference  to 
this  scale.  In  the  case  of  the  rotating  switch  arm  moving  over 
a  series  of  switch  points,  the  switch  points  should  show  the  corre- 
sponding number  of  turns  of  primary  cut  in  when  the  switch 
arms  make  contact  with  these  points. 

The  secondary  is  usually  provided  with  a  number  of  taps  for 


WAVE  LENGTH  OF  THE  RECEIVING  STATION 


51 


cutting  in,  by  means  of  a  switch  arm,  different  numbers  of  turns 
in  the  secondary  circuit.  These  taps  should  be  numbered  with 
the  number  of  turns  for  each  button  in  order  to  distinguish  them; 
or,  better,  they  should  be  marked  to  indicate  the  range  of  wave 
lengths  best  adapted  for  the  button  in  question. 

In  order  to  determine  the  coupling  between  primary  and  second- 
ary used  at  any  time,  a  scale  of  convenient  graduations,  say  tenths 
of  inches,  should  be.  placed  so  that  an  index  carried  by  the  moving 
secondary,  will  travel  over  the  coupling  scale  and  the  coupling 
read  from  this  scale.  The  zero  of  this  scale  should  be  so  placed 
that  when  the  secondary  coil  is  completely  out  of  the  primary, 
the  index  will  stand  opposite  this  zero  mark.  The  zero  mark  of 


FIG.  31. 


the  coupling  scale  does  not  mean  a  zero  coupling  between  the 
two  circuits,  which  would  be  obtained  only  by  separating  the 
coils  by  a  great  distance.  The  greatest  reading  of  the  coupling 
scale  will  be  had  when  the  secondary  is  pushed  completely  into 
the  primary. 

To  calibrate  this  receiving  set,  the  operator  " listens  in"  on 
set,  using  telephone  receivers,  T,  adjusts  his  detector  for  sensi- 
tiveness, couples  wave  meter  with  loop  in  antenna  lead  (see  Fig. 
31),  and  starts  buzzer  going  continuously.  Setting  the  wave 
meter  pointer  at  300  meters  he  adjusts  his  primary  turns,  second- 
ary turns,  and  coupling  until  he  gets  the  strongest  signals  in 
his  receiver  from  the  wave  meter.  These  are  the  adjustments 
necessary  for  300  meters  wave  length.  It  will  be  noticed  that 
there  are  many  possible  combinations  of  primary,  secondary,  and 


52 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


coupling  which  will  give  300  meters.  The  best  adjustment,  in 
order  to  avoid  interference,  will,  as  a  rule,  be  the  one  affording 
the  loosest  possible  coupling  between  the  coils.  Actual  work 
with  the  set  listening  to  stations  having  known  sending  wave 
lengths,  will,  in  practice,  determine  the  best  combination  of  all 
three  variable  elements. 

A  table  of  wave  lengths  should  be  prepared  as  follows: 


Wave  length 
meters 

Primary 

Secondary 

Coupling 

300 

7 

90 

20 

325 

8.5 

90 

22 

350 

10 

90 

24 

and  so  forth,  finding  the  best  adjustments  for  every  25  or  50 
meters  increase  in  wave  length,  up  to  the  limit  of  the  tuner. 

Second  Method. — It  will  have  been  noticed  that  with  untuned 
secondary,  as  in  Fig.  31,  the  tuner  is  usually  in  tune  with  two 
wave  lengths  at  the  same  time,  one  long  and  one  short.  Setting 
the  primary  at  a  given  point,  say  1 1  turns,  and  the  secondary  at 
90  turns,  if  we  examine  the  circuit  with  a  wave  meter,  as  we  pull 
the  secondary  out  of  the  primary,  it  will  be  found  that  changing 
the  coupling  changes  both  the  wave  lengths  to  which  the  set  is  tuned. 
With  primary  and  secondary  unchanged,  take  a  series  of  readings 
with  the  wave  meter  for  every  five  divisions  of  coupling  scale. 
Plot  data  as  shown  in  curves,  Fig.  32.  In  this  case,  curves  were 
plotted,  first  using  the  90  turn  secondary,  then,  the  210  turn 
secondary.  The  effect  of  changing  the  secondary  turns  is  seen 
from  the  curves. 

In  order  to  cover  practically  all  combinations  of  adjustments 
coming  within  the  range  of  the  tuner,  so  as  to  be  able  to -read  at 
once  from  the  tuning  curves  the  wave  lengths  for  any  given  three 
adjustments,  would  require  practically  an  infinite  number  of 
curves.  In  practice  we  would  probably  get  curves  for  every 
10  turns  of  primary,  and  for  all  values  of  coupling  correspond- 
ing to  each  10  turns,  when  using  two  or  three  different  values  of 
secondary.  An  examination  of  a  tuner  made  in  this  manner 
with  a  wave  meter,  will  give  the  greatest  possible  information 
about  the  method  of  operating  it. 

This  method,  however,  involves  considerable  work,  and,  when 
finished,  is  hardly  as  satisfactory,  for  a  permanent  wireless  sta- 


WAVE  LENGTH  OF  THE  RECEIVING  STATION 


53 


tion,  as  that  of  having  a  wave  meter  always  at  hand,  by  means  of 
which  the  receiving  apparatus  can  be  at  once  adjusted  for  any 
wave  length  desired,  or  the  length  of  an  incoming  wave  determined 
at  once  without  reference  to  any  calibration  curve. 


10 


20  30  40  50 

Divisions  of  Coupling  Scale 

FIG.  32. 


Calibration  of  an  Inductive  Type  Receiving  Set  with  Variable 
Condenser  in   Series   or  Parallel,   Secondary   Untuned. — The 

general  method  of  setting  up  different  wave  lengths  is  the  same 
as  in  the  preceding  cases.     The  tabulation  now  includes  another 
variable  element,  the  variable  condenser. 
Tabulate  as  follows: 


54 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


____„ Condenser  in  Series 
Condenser  in  Parallel 


X 


X 


X 


X 


10    20    30   40    50   60   70    80    90  100  110  120  130  140  150  160  170  180 
Degrees  of  Condenser 

FIG.  33. — Coupling  loose,  but  constant  throughout.  Primary  consists 
of  six  steps  of  inductance  numbered  1,  2,  3,  4,  5,  and  6,  respectively.  Sec- 
ondary circuit  untuned. 


WAVE  LENGTH  OF  THE  RECEIVING  STATION 


55 


Wave  length 
meters 

Primary 

Secondary 

Coupling 

Var.  cond. 
series 

Var.  cond. 
parallel 

400 
500 

10 

10 

90 
90 

20 
20 

140° 
180° 



etc.,  for  every  25  or  50  meters  as  desired. 

If  only  one  value  of  the  coupling  be  used  throughout  the 
measurements,  and  only  four  or  five  values  of  primary  used  in 
connection  with  a  variable  condenser,  the  secondary  circuit 
being  aperiodic,  a  set  of  curves  like  that  shown  in  Fig.  33  is  ob- 
tained. These  are  the  curves  of  the  Telefunken  2  kw.  wagon  set 
purchased  for  use  in  the  United  States  Signal  Corps.  It  is  seen 
how  the  wave  lengths  vary  with  the  change  of  the  condenser, 
the  coupling,  primary,  and  secondary,  remaining  unchanged. 

In  operating  this  receiving  set,  and  in  fact  all  inductively 
coupled  receiving  sets,  the  loosest  possible  coupling  should  always 
be  used,  and  both  circuits,  as  far  as  the  variation  of  the  second- 
ary will  permit,  should  be  tuned,  at  this  coupling,  to  the  same 
wave  length,  i.e.,  the  wave  length  of  the  distant  transmitter.  If 
the  coupling  be  changed,  then  both  circuits,  as  far  as  practicable, 
should  be  retuned.  Exact  tuning  of  the  secondary  is  usually 
impracticable  unless  its  inductance  is  shunted  with  a. variable 
condenser. 

Calibration  of  Inductive  Type  Receiving  Set  with  Tuned 
Secondary. — The  object  is  to  calibrate  both  circuits  of  the  receiv- 
ing set  independently,  so  as  to  be  able  to  set  both  of  them  for  the 
same  wave  length,  and,  by  using  the  loosest  possible  coupling, 
have  the  station  tuned  to  but  one  wave  length  at  a  time,  and  by 
these  means,  not  only  avoid  interference,  but  reduce  the  effects 
of  static  and  atmospheric  discharges  to  a  minimum.  This 
calibration  is  absolutely  necessary  if  the  receiving  apparatus  is 
to  be  used  for  reading  signals  from  stations  sending  out  sus- 
tained or  practically  undamped  oscillations.  A  variable  air 
condenser  of  about  0.002  mfd.  maximum  capacity  is  connected 
in  parallel  with  the  secondary,  Fig.  35,  and  this  circuit  is  tuned 
by  varying  the  condenser. 

Calibration  of  the  Antenna  Circuit. — Couple  an  untuned  sec- 
ondary circuit,  as  shown  in  Fig.  31,  as  loosely  as  possible  with  the 
primary,  and  then  with  wave  meter  set  up  waves  of  different 
lengths  varying  the  primary  or  antenna  circuit,  and  listening 


56 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


for  maximum  sound  in  the  telephone  receivers  at  the  resonance 
position,  when  the  antenna  is  tuned  to  the  same  wave  length 
as  the  wave  meter. 

Tabulate  turns  necessary  for  various  wave  lengths  as  follows: 


Wave  length 
meters  . 

Primary  turns 

350 
400 
450 
500 

4 
7 
10 
13 

and  so  forth,  up  to  the  limit  of  the  primary  coil. 

Another  method,  due  to  Professor  Pierce,  is  shown  in  Fig. 
34,  where  the  primary  is  excited  by  a  nearby  wave  meter  with 
attached  buzzer.  A  detector  with  telephone  receiver  in  shunt  is 
unilaterally  connected  to  the  primary  circuit  as  shown.  If  the 


V 

c 

B 


Wm. 


FIG.     34. — Calibration    of    primary,      FIG.  35. — Calibration  of  secondary. 
Pierce's  method. 

sound  is  too  faint  with  detector  attached  as  in  diagram,  move 
connection  to  B  or  C. 

Calibration  of  the  Secondary  Circuit. — The  antenna  and 
ground  are  then  disconnected  from  the  primary,  P,  of  tuner 
(Fig.  35).  Secondary,  S,  to  the  terminals  of  which  the  variable 
condenser,  V,  is  connected,  is  loosely  coupled  with  wave  meter, 
Wj  and  different  numbers  of  turns  of  secondary  are  cut  in  by  the 
switch,  and  the  number  of  degrees  of  condenser  with  a  fixed 
value  of  secondary  necessary  for  different  values  of  wave  lengths 


WAVE  LENGTH  OF  THE  RECEIVING  STATION 


57 


determined  by  listening  for  maximum  sound  in  telephone,  T. 
The  coupling  between  the  wave  meter  and  receiving  set  should 
be  made  so  loose  that  the  maximum  sound  occurs  during  only  a 
slight  change  of  the  variable  element.  Tabulate  results  as 
follows : 

DEGREES  OF  CONDENSER  NECESSARY  TO  PRODUCE  VARIOUS 

WAVE    LENGTHS    WITH    DIFFERENT    NUMBERS    OF 

SECONDARY  TURNS 


Wave  length 
meters 

25  turns 

50  turns 

90  turns 

210  turns 

400 

7  5° 

500 

19° 

6.5° 

600 

29° 

10° 

700 

40  5° 

14° 

800 
900 

54.5° 
70° 

18° 
23.5° 

8° 
9.5° 



1000 

82° 

29° 

12° 

1100 

35° 

14.5° 

1200 

42° 

17.5° 

1300 

49° 

21  5° 

1400 

57° 

25° 

7.5° 

These  results  may  be  plotted  as  curves,  making  a  curve  for 
each  value  of  secondary  inductance,  and  plotting  wave  lengths 
in  meters  as  ordinates,  and  degrees  of  condenser  scale  as  abscissae. 


FIG.  36. — Calibration  of  secondary. 

Another  method  is  shown  in  Fig.  36.  Connect  a  detector 
with  telephone  in  parallel  with  it,  unilaterally  to  the  secondary, 
and  excite  the  circuit  with  the  wave  meter. 

Measurement  of  Incoming  Wave  from  a  Distant  Sending 
Station. — Tune  your  own  receiving  apparatus  as  sharply  as 


58  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

possible  to  the  incoming  wave,  getting  the  maximum  strength 
of  signals  in  your  telephone  receivers.  The  wave  meter  is  coupled 
to  the  antenna  as  in  Fig.  31,  and  when  the  signals  from  the  dis- 
tant station  have  ceased,  the  buzzer  is  started  giving  a  continu- 
ous signal,  and  the  inductance  and  capacity  of  the  wave  meter, 
W,  are  varied  until  the  sound  from  the  buzzer  heard  in  the  tele- 
phone of  the  receiving  set  is  a  maximum,  when  the  wave  meter 
is  tuned  to  the  receiving  circuit. 

The  coupling  is  made  so  slight  that  the  maximum  sound  occurs 
during  only  a  slight  change  of  the  capacity.  Then  the  reading 
of  the  wave  meter  is  the  wave  length  of  the  distant  station. 

If  two  wave  lengths  are  observed  due  to  close  coupling  of 
primary  and  secondary  of  the  receiving  apparatus,  note  both 
readings.  To  determine  which  is  correct  wave  length,  again 
tune  to  the  distant  station  using  a  different  amount  of  primary 
and  a  different  coupling  the  second  time.  The  correct  reading 
will  remain  as  before,  but  the  false  one  will  have  a  different 
value:  or,  better  still,  if  using  an  inductively  coupled  set  with 
variable  primary  and  variable  secondary,  vary  all  the  elements 
— primary  inductance,  secondary  inductance,  and  condenser 
shunting  secondary,  and,  when  the  set  is  tuned  to  the  distant 
station  with  the  loosest  possible  coupling,  it  will  be  found  that 
it  is  in  resonance  with  only  one  wave  length,  which  is  that  of 
the  distant  station. 


CHAPTER  VII 
MEASUREMENT  OF  CAPACITY  AND  INDUCTANCE 

Capacity  of  a  Condenser  by  the  Substitution  Method. — This 
supposes  the  possession  of  a  calibrated,  variable  condenser. 

A  closed  oscillatory  circuit  is  made  with  any  desired  inductance 
L  (see  Fig.  37),  and  the  unknown  capacity  Cx.  Then  an  aperi- 


cx 


FIG.  37. — Measurement  of  capacity,  substitution  method. 

odic  receiving  circuit  is  coupled  very  loosely  to  the  closed  oscilla- 
tory circuit,  or  better,  as  Prof.  Pierce  suggests,  connect  a  detector 
and  telephone  unilaterally  to  the  circuit  to  be  measured,  as  in 


cv 


FIG.  38. 

Fig.  38.  The  wave  meter,  W,  is  used  as  a  sending  set  and  tuned 
to  the  above-mentioned  closed  oscillatory  circuit.  Resonance 
is  obtained  when  the  sound  in  the  receiver  is  loudest,  and  this  will 
correspond  to  some  distinct  position  of  the  variable  condenser 

59 


60 


WAVE  METER  IN  WIRELESS  TELEGRAPHY 


of  the  wave  meter.  Then  the  variable  condenser  Cv  is  put  in 
the  circuit  instead  of  Cx.  Cv  is  varied  until  the  two  circuits  are 
in  tune,  the  wave  meter  circuit  being  kept  as  it  was  when  used 
with  Cx.  The  value  of  the  capacity  of  Cv  is  then  equal  to  the 
unknown  capacity  Cx,  and  if  Cv  is  calibrated  directly  in  centi- 
meters or  microfarads,  or  if  a  calibration  curve  is  at  hand  show- 


w 


t 


FIG.  39. — Measurement  of  capacity. 

ing  the  values  in  microfarads  or  in  centimeters  for  every  setting 
in  degrees  of  the  condenser  scale  of  Cv,  the  value  of  Cx  is  at  once 
known. 

Capacity  of  a  Condenser  in  an  Oscillatory  Circuit  with  a  Known 
Inductance. — A  closed  oscillatory  circuit  is  made  with  a  known 
inductance  and  the  unknown  condenser  Cx  (Fig.  39). 


w 


CX 


o)Tel. 


FIG.  40. — Measurement  of  capacity,  Pierce. 

The  aperiodic  circuit,  A,  is  very  loosely  coupled  with  the  closed 
oscillatory  circuit,  or  a  detector  and  telephone  is  unilaterally 
connected  to  the  circuit  to  be  measured  as  in  Fig.  40  and  the  wave 
meter,  W,  is  used  as  an  oscillator  and  tuned  to  the  closed  oscilla- 
tory circuit  L,  Cx.  Then  the  value  of  wave  length  obtained 
when  the  loudest  sound  is  heard  in  the  receivers,  and  the  value 


MEASUREMENT  OF  CAPACITY  AND  INDUCTANCE       61 
of  the  known  inductance,  are  substituted  in  the  following  formula : 
^  meters  =  59.6\/C  mfds.  XL  cm. 

and  the  equation  solved  for  C. 

Thus  the  wave  length  for  resonance  equals  534  m.  and  the 
known  inductance  is  20,000  cm.     To  find  the  unknown  capacity. 


C  mfds.  = 


'X  metersx  2 
v    59.6    / 


L  cm. 
Cx  =  0.004  mfds. 


80 
20000 


To  avoid  the  labor  of  dividing  and  extracting  the  square  root, 
etc.,  it  is  more  convenient  to  refer  to  the  logarithmic  chart  (see 
Fig.  42).  Instructions  for  use  will  be  found  with  the  chart. 
This  method  of  measuring  capacity  is  correct  only  when  the 
capacity  of  the  wire  of  which  inductance  L  is  constructed,  is 
negligible.  This  is  not  the  case  when  inductance  L  is  the  primary 
or  secondary  of  a  receiving  set,  or  the  inductance  coil  of  a  wave 
meter,  or  an  inductance  of  similar  size. 


o 

o 

o 

o 

c 

0 

o 

0 

o 

C 

o 

0 

FIG.  41. — Measurement  of  the  capacity  of  the  Antenna. 

Measurement  of  the  Capacity  of  the  Antenna. — The  antenna 
circuit,  Fig.  41,  is  excited  by  placing  an  open  spark  gap  directly 
between  antenna  A  and  ground,  the  spark  gap  being  directly 
across  the  terminals  of  the  secondary  of  the  transformer,  con- 
denser and  helix  being  cut  out  of  circuit  as  when  measuring  the 
natural  wave  length  of  the  antenna. 


62  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

A  large  capacity,  C,  and  a  small  inductance,  L,  are  connected 
by  means  of  a  three-point  switch,  so  that  they  can  readily  be  cut 
into  the  antenna  circuit  as  shown. 

Let  the  natural  wave  length  of  the  antenna  itself  be  called  Xa. 
Suppose  the  wave  length  changes  to  Xc  or  h  on  the  insertion 
of  the  capacity,  C,  or  inductance,  L,  respectively.  If  the  inserted 
capacity  and  inductance  are  so  chosen  that  the  wave  lengths  do 
not  differ  by  a  large  amount,  then  the  measurements  of  the  three 
wave  lengths  will  allow  a  closely  approximate  calculation  of  the 
capacity  of  the  antenna,  as  follows: 


^  _0        AC    ...o/^vx 


j 


20L 
and, 

n  _Cc-j-Ci 
2 

Buzzer  excitation  may  also  be  used. 

Determination  of  the  Coefficient  of  Self-inductance.  —  This 
supposes  the  possession  of  a  condenser  of  known  capacity. 

A  closed  oscillatory  circuit  is  constructed  out  of  a  known 
capacity,  C,  and  an  unknown  inductance,  L.  An  aperiodic 
receiving  circuit  is  coupled  with  the  above-mentioned  closed 
oscillatory  circuit,  and  the  wave  meter  tuned  to  the  latter  circuit 
as  in  determining  an  unknown  capacity  (Fig.  39)  or  a  unilaterally 
connected  detector  and  telephone  may  be  employed  as  shown  in 
Fig.  40.  The  wave  length  at  resonance  is  read  from  the  wave 
meter.  The  known  capacity  being  in  mfds.,  the  wave  length  in 
meters,  and  the  unknown  inductance  in  centimeters,  we  can  find 
the  value  L  from  the  formula: 


59.6 


C  mfds. 


or,  what  is  quicker  and  more  convenient,  find  it  by  means  of  the 
logarithmic  chart  (see  Fig.  42  and  accompanying  explanation). 
This  method  is  correct  only  when  the  capacity  of  the  unknown 
inductance  itself  is  negligible,  or  is  known  and  added  to  the  value 
of  the  known  capacity  in  the  formula. 


MEASUREMENT  OF  CAPACITY  AND  INDUCTANCE       63 

Measurement  of  the  Coefficient  of  Mutual  Inductance.  —  This 
measurement  may,  at  times,  be  necessary  for  determining  the 
mutual  inductance  between  the  primary  and  secondary  of  a 
receiving  oscillation  transformer  or  loosely  coupled  tuning  coil. 

A  closed  oscillatory  circuit  consisting  of  a  condenser  of  known 
capacity  and  the  unknown  inductance  to  be  measured,  is  con- 
nected as  hereinafter  described,  acted  upon  by  a  wave  meter 
which  is  tuned  to  the  'wave  length  of  the  circuit  containing  the 
unknown  inductance,  and  the  resonance  point  determined  by  the 
maximum  sound  in  the  receivers  of  an  aperiodic  circuit  loosely 
coupled  with  the  inductance  under  examination. 

The  two  coils,  in  whatever  relative  position  to  each  other  it  is 
desired  to  measure  their  mutual  inductance,  are  first  connected 
in  series  with  each  other  and  with  the  known  capacity,  so  that 
the  current  flows  in  the  same  direction  around  both  coils,  and 
the  inductance,  LI,  is  determined  by  wave  metrical  method. 
They  are  then  joined  in,  series  with  each  other  and  with  a  known 
capacity,  so  that  the  current  will  flow  in  opposite  directions 
around  both  coils,  and  the  inductance  L2  then  determined  by 
examination  with  a  wave  meter.  Then  the  formula  connecting 
the  mutual  inductance,  M,  of  these  coils,  with  the  two  inductances 
just  measured,  is  as  follows: 


Hence,  given  two  coils,  we  can  measure  their  mutual  inductance 
in  any  position  with  respect  to  each  other. 

The  mutual  inductance  of  a  transmitting  oscillation  trans- 
former can  also  be  measured  by  the  above  method. 

Determination  of  the  Coefficient  of  Coupling.  —  This  is  an  im- 
portant determination  to  be  made  at  times  in  the  case  of  the 
receiving  transformer.  It  may  be  shown  that  the  coefficient  of 
coupling  of  two  coils,  T,  is  equal  to  the  quotient  of  the  mutual 
inductance  of  the  two  coils  in  any  position,  by  the  square  root 
of  the  product  of  the  separate  inductances  of  the  two  coils,  that  is, 

M 

= 


So,  by  the  methods  before  given,  we  can  measure  the  induct- 
ances L  p  and  Ls,  separately,  by  connection  to  a  known  capacity, 
and  then  measure  the  mutual  inductance,  M,  as  described  above, 


64  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

and,  placing  the  values  found  in  the  formula,  we  get  the  true 
coefficient  of  the  coupling  between  the  two  coils. 

Use  of  the  Logarithmic  Chart  for  Calculating  the  Frequency, 
Wave  Length,  Inductance  and  Capacity  of  Oscillatory  Circuits. — 
Where  many  calculations  are  required,  instead  of  solving  the 
formulae  before  given,  it  is  simpler,  and,  in  general,  sufficiently 
satisfactory  to  take  the  values  desired  from  Fig.  42. 

This  chart  gives  directly  the  values  of  wave  lengths  from  300 
to  3000  meters,  with  corresponding  frequencies  from  1,000,000 
cycles  to  100,000  cycles;  for  capacities  from  0.0025  to  0.025  mfds: 
and  for  inductances  from  10,000  to  100,000  cm.  As  will  be 
shown  later  it  can  be  applied  to  values  of  the  variables  other 
than  those  appearing  on  the  chart. 

To  use  the  chart  a  straight  edge  is  placed  so  as  to  cross  the 
selected  value  of  the  known  capacity  on  the  capacity  scale  and 
the  wave  length  read  from  the  wave  meter,  on  the  scale  of  wave 
lengths;  when  the  inductance  is  at  once -read  from  the  intersec- 
tion of  the  straight  edge  with  the  inductance  scale. 

Case  1. — Capacity  and  inductance  known,  to  determine  the 
wave  length. 

C  =  0.005  mfds.  L  =  55,800  cm. 

The  straight  edge  placed  on  these  values  crosses  the  wave 
length  scale  at  1000  meters;  hence,  this  is  the  required  wave 
length. 

Case  2. — Knowing  the  wave  length  to  determine  the  corre- 
sponding frequency. 

-4  =  600.  The  corresponding  frequency  lying  beside  it  on  the 
adjoining  scale  is  500,000  cycles. 

Case  3. — Knowing  the  wave  length  and  capacity,  to  find  the 
corresponding  inductance. 

/I  =  900  C  =  0.019  mfds. 

The  straight  edge  placed  to  cross  the  wave  length  scale  at  900 
meters  and  the  capacity  scale  at  0.019  cuts  the  inductance  scale 
at  12,000  cm.,  the  required  inductance. 

Corrections  for  Values  of  Inductance  or  Capacity  Greater 
or  Less  than  the  Values  Given  on  the  Chart. — From  the  formula 
-4  =  59.6  VL  cm.  X  C  mfds.  it  is  seen  that  the  wave  length 
varies  directly  as  the  square  root  of  both  the  inductance  and  the 


MEASUREMENT  OF  CAPACITY  AND  INDUCTANCE       65 


1QQOO 


15000 


20000 


40000 


50000 


60000 


70000 


80000 


300  =t=.  1000000 


§  1000- 

1 


900- 


700000 


500-3=- 600000 


-500000 


400000 


•200000 


150000 


100000 


.0025- 


.004- 


.01 


.015- 


FIG.  42. — Logarithmic  chart. 


66  WAVE  METER  IN  WIRELESS  TELEGRAPHY 

capacity:  so,  if  either  the  inductance  or  the  capacity  be  multi- 
plied by  any  number,  the  wave  length  is  to  be  multiplied  by  the 
square  root  of  that  number. 

A  capacity  100  times  as  large  as  the  value  shown  on  the  chart 
would,  with  the  given  inductance,  produce  a  wave  length  10 
times  the  value  shown  by  the  intersection  of  the  straight  edge 
with  the  scale  of  wave  lengths,  and  a  corresponding  frequency 
of  one-tenth  of  the  value  indicated  by  the  frequency  scale. 

Case  4.-— C=l  mfd.  and  L  =  63,500  cm.  What  will  be  the 
resulting  wave  length  and  frequency? 

1  mfd.  =0.01  mfd.XlOO 

Setting  the  straight  edge  to  intersect  the  capacity  scale  at 
0.01  mfds.,  and  the  inductance  scale  at  63,500  cm.,  the  straight 
edge  intersects  the  wave  length  scale  at  1500  meters.  Multi- 
plying this  by  10  gives  15,000  meters,  the  required  wave  length. 
One-tenth  of  the  frequency,  200,000,  corresponding  to  the  1500 
meter  wave  length,  will  be  the  frequency  for  15,000  meters. 

In  case  the  chosen  capacity  or  inductance  is  ten  times,  or  one- 
tenth  as  large  as  any  value  on  the  chart,  the  wave  length  read 
from  the  chart  will  have  to  be  multiplied  or  divided  by  the  square 
root  of  10,  or  3.162.  This  multiplication  or  division  may  be 
performed  graphically  as  follows: 

From  the  point  on  the  chart  where  the  straight  edge  crosses 
the  wave  length  scale,  lay  off  on  this  scale  a  distance  equal  to 
one-half  the  length  of  the  scale.  This  distance  is  laid  off  to 
whichever  side  makes  it  fall  completely  on  the  scale.  The  point 
thus  found  will  be  the  desired  wave  length.  Laying  off  the  half 
scale  length  to  the  right  divides  the  wave  length  value  by  the 
square  root  of  10,  and  laying  it  off  to  the  left  multiplies  by 
that  value.  As  the  result  obtained  by  multiplying  by  the  square 
root  of  10  is  10  times  as  great  as  the  result  obtained  by  dividing 
by  the  square  root  of  10,  it  will  be  necessary,  in  order  to  get  a 
correct  result,  where  we  have  been  obliged  to  lay  the  distance 
off  to  the  left,  instead  of  to  the  right  as  desired,  to  divide  the  result 
obtained  from  the  chart  by  10. 

Case  5.— C  =  0.001  mfd.  and  L  =  20,000  cm.  What  wave 
length  will  result? 

Intersection  at  842  meters.  To  get  correct  result  we  must 
divide  the  result  by  the  square  root  of  10  =  3.162.  Lay  off  one- 
half  length  of  wave  length  scale  from  842  to  left,  since  it  cannot 


MEASUREMENT  OF  CAPACITY  AND  INDUCTANCE'''  '6^ 

be  placed  to  the  right.  This  gives  the  wave  length  as  2660 
meters  which  is  10  times  too  large,  since  to  divide  we  should 
have  laid  off  the  distance  to  the  right,  hence,  2660-^10  =  266 
meters,  the  correct  wave  length. 

Case  6. — Measurement  of  inductance.  C  =  0.001  mfd.  A  = 
3000  meters.  What  is  the  value  of  inductance? 

Lay  off  from  3000  meters  to  the  right  on  the  middle  scale  a 
distance  equal  to  one-half  the  scale  of  wave  lengths.  This  point 
is  approximately  950  meters.  A  straight  edge  placed  on  this 
point  and  the  capacity  0.01  (a  reading  on  the  scale  10  times 
larger  than  the  value  of  the  known  capacity),  will  intersect  the 
inductance  scale  at  25,200  cm.  This  reading  must  be  multiplied 
by  10  to  give  the  correct  reading,  252,000  cm. 

Case  7. — Measurement  of  capacity. 

Known  inductance  =  15,000  cm.     ^  =  300  meters.     Capacity? 

From  300  lay  off  a  distance  equal  to  one-half  the  length  of 
wave  length  scale.  This  locates  a  point  950  meters,  on  which 
place  straight  edge  which  has  been  pivoted  on  point  on  inductance 
scale  marked  15,000  cm.  The  straight  edge  intersects  the 
capacity  scale  at  0.017  mfds.  To  obtain  the  correct  reading  it 
is  evident  that  it  is  necessary  to  take  one-tenth  of  this  reading, 
since  10  times  the  capacity  was  used.  The  true  reading  is, 
therefore,  0.0017  mfds. 

Case  8. — Where  values  of  neither  inductance,  capacity  or  wave 
length  are  found  on  the  chart. 

The  capacity  of  an  antenna  is  0.001  mfds.  What  must  be  the 
value  of  the  inductance  in  circuit,  that  the  wave  length  may  be 
5000  meters? 

500  meters  is  one-tenth  of  the  value  of  the  true  wave  length. 

0.01  mfds.  is  10  times  the  value  of  the  real  capacity. 

Lay  off  one-half  of  wave  length  scale  from  500  meters.  This 
gives  a  point,  1572  meters,  through  which  a  straight  line  from 
0.01  on  the  capacity  scale  gives  70,225  cm.  as  the  intersection 
on  the  inductance  scale.  Since  10  times  the  real  value  of  the 
condenser,  and  only  one-tenth  of  the  value  of  the  wave  length 
were  used,  the  inductance  will  be  10X10,  or  100  times  as  great 
as  the  value  read  from  the  scale,  or,  7,022,500  cm.  or  7.0225 
millihenrys. 


INDEX 

A 

PAGE 

Adjustment  of  the  sending  station  to  comply  with  the    Act  to  Regu- 
late Radio  Communication 45 

Alternating  current,  definition  of 1 

Alternation,  definition  of 2 

Ammeter,  hot-wire,  as  indicating  device 6 

precautions  in  use  of 28 

Amplitude,  definition  of 1 

Antenna  circuit  of  transmitter,  determination  of  wave  length  of.  . .  .22,  25 

Antenna,  measurement  of  capacity  of 61 

Aperiodic  circuit,  as  indicating  device 7 

definition  of 2 

supplied  with  Telefunken  meters 13 

B 

Buzzer  attachments  for  wave  meter 9 

C 

Calibration  of  receiving  set  having  double-slide  tuner 49 

inductive  type  receiving  set  having  an  untuned  second- 
ary and  variable  primary 50-53 

inductive  type  receiving  set  with  variable  condenser  in .  9 

series  or  parallel,  secondary  untuned 53 

inductive  type  receiving  set  with  tuned  secondary 55-57 

Capacity  and  inductance,  measurement  of 59 

measurement,  substitution  method 59 

of  condenser  in  circuit  with  known  inductance,  measurement 

of 60 

of  antenna,  measurement  of 61 

Chart,  logarithmic,  use  of,  for  calculating  frequency,  wave  length,  induc- 
tance and  capacity 64-67 

Circuit,  aperiodic,  defined 2 

as  indicating  device 7 

supplied  w^th  Telefunken  meters 13 

Circuit  of  wave  meter,  elementary 5 

oscillatory,  defined ! 

Circuits,  syntonic 3 

Closed  oscillatory  circuit,  measurement  of  damping  of 34 

Coefficient  of  self -inductance,  determination  of 62 

Coefficient  of  mutual  inductance,  measurement  of 63 

69 


70  INDEX 

PAGE 

Coupled  system,  measurement  of  damping  of 44 

Coupling,  coefficient  of,  equation 30 

receiving  transformer 63 

Coupling,  loose  and  close,  effect  of,  on  emitted  waves 28 

Coupling,  percentage  of,  calculation 29 

different  from  coefficient  of  coupling 30 

Curves  reasonance,  method  of  obtaining 27,  28 

Curves,  tuning,  of  sending  station 23,  24 

Cycle,  definition  of 2 

.  '      D  '  '    :.  * 

Damped  oscillations,  definition  of 2 

Damping  and  logarithmic  decrement,  measurement  of 31 

Damping  factor,  definition  of 2 

Damping  of  closed  oscillatory  circuit,  measurement  of 34 

Damping  of  wave  meter,  determination  of 40 

using  thermo-element  and  galvanometer ....  41 

using  ther mo-am  meter 42 

using  hot-wire  wattmeter 43 

using  condenser  formulae. 43 

Decrement,  logarithmic,  definition  of 2 

care  to  be  exercised  in  making  measurements 

of 40,44 

V.  Bjerknes'  formula  for 35 

simplified  formula 35 

combined     and    simplified     formula     using 

capacity  readings 36 

measurement  with  thermo-element  and  gal- 
vanometer   36 

measurement  using  thermo-ammeter 37 

measurement  using  hot-wire  wattmeter 37 

measurement  using  condenser  readings 37-39 

of  coupled  system,  measurement  of 44 

of  coupled  system,  reduction  of 45 

of  radiating  circuits,  legal  limit 31,  46 

Decremeter,  Marconi 31 

Definitions 1-4 

Detector,  crystal,  as  indicating  device 7 

Dynamometer  telephone,  Pierce 7 

• 
E 

Equation,  fundamental,  of  wireless  telegraphy 3 

Exciting  circuit  of  transmitter,  measurement  of  wave  lengths  of 23 

F 

Feebly  damped  train  of  oscillations 2 


INDEX  71 

PAGE 

Frequency,  definition  of 2 

Fundamental  equation  of  wireless  telegraphy 3 

G 

Galvanometer  and  detector,  calibration  of 

measurement  with 21 

Galvanometer  and  thermo-element 7 

General  remarks , .  1 

H 

Helium  tube 5 

Highly  damped  train  of  oscillations 2 

Hot-wire  meters,  precautions  in  use  of 28 

Hump,  lower 27 

upper 26 

I 

Incoming  wave  from  distant  sending  station,  measurement  of 57 

Inductance  and  capacity,  measurement  of 59 

Induction  coil  and  spark  gap,  use  with  Pierce  meter 9 

L 

Logarithmic  chart,  use  of  for   calculating  frequency,    wave   length, 

inductance  and  capacity 64^67 

Logarithmic  decrement  defined 2,  31 

measurement  of 31-34 

V.  Bjerknes'  formula  for 35 

simplified  formula 35 

combined  and  simplified  formla  using  capacity 

readings 36 

measurement  with  galvanometer  and  thermo- 
element   36 

measurement  using  thermo-ammeter 37 

measurement  using  hot-wire  wattmeter 37 

measurement  using  condenser  readings 37-39 

of  coupled  system,  reduction  of 45 

Loose-coupling,  effect  of,  on  emitted  waves 28 

M 

Measurement  of  capacity  and  inductance 59 

substitution  method 59 

of  a  condenser    in  circuit    with  a  known 

inductance 60 

of  the  antenna.  .  61 


72  INDEX 

PAGE 

Measurement  of  coefficient  of  mutual  inductance 63 

damping  of  a  coupled  system 44 

damping  of  a  closed  oscillatory  circuit 34 

incoming  wave  from  distant  sending  station 57 

radiated  wave  lengths  of  coupled  system 26 

self-damping  of  wave  meter 40 

using  thermo-element  and 

galvanometer 41 

using  thermo-ammeter ...  42 

using  hot-wire  wattmeter.  43 

using  condenser  formulae  .  .  43 

sending  wave  lengths,  general  remarks 20 

wave  lengths  of  receiving  station,  general  remarks 48 

Measurement  with  helium  tube. 20 

telephone  and  detector,  or  galvanometer  and  de- 
tector   21 

N 

Natural  period,  definition  of 23 

Natural  wave  length,  definition  of 23 

measurement  of 23 

O 

Operation  of  inductively  coupled  receiving  set,  general  remarks 55 

Oscillation  constant,  definition  of 3 

Oscillations,  complete,  determination  of  approximate  number  in  a 

wave  train 44 

Oscillations,  damped,  definition  of 

Oscillatory  circuit  defined , 2 

P 

Percentage  of  coupling  of  circuits,  calculation  of 29 

Period,  definition  of 

Period,  natural,  definition  of 23 

Principle  of  operation  of  the  wave  meter 

Pure  wave,  method  of  determining  whether  station  is  emitting 45 


Quenched  spark  apparatus,  measurement  of  antenna  wave  length  of .  .  23,  29 
with  variometers,  precautions  to  be  taken 

during  measurements 29 

R 

Radiated  waves  of  coupled  system,  correct  measurement  of 26 

Radiating  circuits,  legal  limit  of  logarithmic  decrement  of 31,  46 


INDEX  73 

PAGE 

Receiving  set  with  double-slide  tuner,  calibration  of 49 

inductive  type  having  untuned  secondary  and  variable 

primary,  calibration  of 50-53 

inductive  type  with  variable  condenser  in  series  or  par- 
allel, secondary  untuned,  calibration  of 53—55 

inductively  coupled,  generalre  marks  concerning  meth- 
od of  operation 55 

inductive  type  with  tuned  secondary,  calibration 55-57 

Receiving  transformer,  determination  of  coefficient  of  coupling 63 

Reasonance  curves,  method  of  obtaining 27,  28 

Reasonance,  definition  of 3 

S 

Self-damping  of  wave  meter,  determination  of 40-43 

Self-inductance,  coefficient  of,  determination  of 62 

Sending  station,  tuning  of 22 

method  of   procedure  in  adjustment  of,  to  comply 

with  the  Act  to  Regulate  Radio  Communication  45 
method  of  adjustment  where  wave  length   is   not 

restricted  by  law  or  official  order 46 

Spark  gap  as  indicator  of  resonance 5 

determination  of  resistance  of 44 

of  sending  station,  adjustment  of,  while  measuring  wave 

length  of  antenna  circuit  alone 22 

Syntonic  circuits 3 

T 

Telephone  and  detector,  measurement  with 21 

Telephone,   dynamometer 7 

Thermo-ammeter,  Duddell 6,  32 

Thermo-element  and  galvanometer  as  indicating  device 6 

calibration  of 33 

Thermo-element,  construction  of 32 

Tuning  curves  of  transmitter,  method  of  securing 23,  24 

Tuning,  definition  of 4 

Tuning  the  sending  station 22 

Types  of  wave  meters  in  use  in  the  U.  S.  Signal  Corps 11 

U 

Undamped  oscillations,  definitions  of 2 

V 

Variometers  in  quenched  spark  circuits,  precautions 29 


74  INDEX 

W 

PAGE 

Wattmeter,  hot-wire,  precautions  in  use  of 28 

for  measuring  decrement 32 

Wave  length,  best  for  transmitter,  determination  of 46 

equation 4 

of  antenna  circuit,  sending  set,  determination  of 22,  25 

natural,  definition  of 23 

natural,  measurement  of 23 

of  receiving  station,  measurement  of,  general  remarks  .  48 

Wave  lengths,  sending,  measurement  of 20 

measurement  with  helium  tube 21 

of  coupled  system 26 

Wave  meter  as  a  receiving  device 5 

as  a  sending  set 8 

circuit,  elementary 5 

energy-indicating  devices  for 5 

Pierce,  diagram  of  connections  and  description  of 11 

principle  of  operation 4 

Telefunken,  type  E.KI.W,  description  of 12 

Telefunken,  type  E.G.W 17 

values  of  self-damping  of 39.  40 

type  E.Ki.Wk.,  description  of 15 

used  as  a  receiving  set,  general  remarks 20 

used  for  training  new  operators  in  use  of  receiving 

apparatus 49 


&?.. 

100   * 


YG 


749205 


Go?. 2 

Engineering 
Library 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


